Regulated Operations [Abstract]
Permissible limit on debt to total capital percentage
Debt Instrument Covenant Debt To Capital Percentage
Debt instrument covenant debt to capital percentage.
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Current Assets
Schedule of Other Current Assets [Table Text Block]
Income Tax Disclosure [Abstract]
Deferred Income Tax Assets And Liabilities [Table]
Deferred Income Tax Assets And Liabilities [Table]
Deferred Income Tax Assets And Liabilities [Table]
Tax Period [Axis]
Tax Period [Axis]
Tax Period [Domain]
Tax Period [Domain]
2034 [Member]
Two thousand and Thirty four expiry [Member]
Two thousand and thirty four expiry.
2035 [Member]
Two thousand and thirty five expiry [Member]
Two thousand and thirty five expiry.
2036 [Member]
Two thousand and thirty six expiry [Member]
Two thousand and thirty six expiry.
2037 [Member]
Two Thousand And Thirty Seven Expiry [Member]
Two Thousand And Thirty Seven Expiry [Member]
2038 [Member]
Two Thousand And Thirty Eight Expiry [Member]
Two Thousand And Thirty Eight Expiry [Member]
2039 [Member]
Two Thousand And Thirty Nine Expiry [Member]
Two Thousand And Thirty Nine Expiry [Member]
Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Income Tax Assets And Liabilities [Line Items]
Total losses
Non capital losses carried forward to reduce future period taxable income
Non-capital losses carried forward to reduce future period taxable income.
Debt Disclosure [Abstract]
Line of Credit Facility [Table]
Line of Credit Facility [Table]
Legal Entity [Axis]
Legal Entity [Axis]
Entity [Domain]
Entity [Domain]
Hydro One Inc. [Member]
Hydro One Inc. [Member]
Hydro One Inc. [Member]
Credit Facility [Axis]
Credit Facility [Axis]
Credit Facility [Domain]
Credit Facility [Domain]
Revolving Credit Facility [Member]
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility [Line Items]
Maximum borrowing capacity
Line of Credit Facility, Maximum Borrowing Capacity
Amount Drawn
Long-term Line of Credit
Earnings Per Share [Abstract]
Earnings Per Common Share
Earnings Per Share [Text Block]
Net income (loss) attributable to common shareholders (millions of dollars)
Net Income (Loss) Available to Common Stockholders, Basic
Weighted average number of shares
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Basic (in shares)
Weighted Average Number of Shares Outstanding, Basic
Effect of dilutive stock-based compensation plans (in shares)
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements
Diluted (in shares)
Weighted Average Number of Shares Outstanding, Diluted
EPS
Earnings Per Share, Basic [Abstract]
Basic (in dollars per share)
Earnings Per Share, Basic
Diluted (in dollars per share)
Earnings Per Share, Diluted
Accounting Policies [Abstract]
Average Service Lives and Depreciation and Amortization Rates
Depreciation Depletion And Amortization Methods And Rates Of Property Plant And Equipment [Table Text Block]
Depreciation Depletion And Amortization Methods And Rates Of Property Plant And Equipment
Retirement Benefits [Abstract]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Table]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Table]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Table]
Retirement Plan Type [Axis]
Retirement Plan Type [Axis]
Retirement Plan Type [Domain]
Retirement Plan Type [Domain]
Post-Retirement and Post-Employment Benefits [Member]
Other Postretirement Benefits Plan [Member]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Line Items]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Line Items]
Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Line Items]
Effect of a 1% increase in health care cost trends
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation
Effect of a 1% decrease in health care cost trends
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation
Basis of Consolidation
Basis Of Consolidation [Policy Text Block]
Basis Of Consolidation Policy [Text Block]
Basis of Accounting
Basis of Accounting, Policy [Policy Text Block]
Use of Management Estimates
Use of Estimates, Policy [Policy Text Block]
Regulatory Accounting
Regulatory Accounting [Policy Text Block]
Regulatory Accounting Policy [Text Block]
Cash and Cash Equivalents
Cash and Cash Equivalents, Policy [Policy Text Block]
Revenue Recognition
Revenue from Contract with Customer [Policy Text Block]
Accounts Receivable and Allowance for Doubtful Accounts
Accounts Receivable And Allowance For Doubtful Accounts [Policy Text Block]
Accounts Receivable And Allowance For Doubtful Accounts Policy [Text Block]
Noncontrolling interest
Noncontrolling Interest [Policy Text Block]
Noncontrolling Interest Policy [Text Block]
Income Taxes
Income Tax, Policy [Policy Text Block]
Materials and Supplies
Materials And Supplies Policy [Policy Text Block]
Materials And Supplies Policy [Policy Text Block]
Property, Plant and Equipment
Property, Plant and Equipment, Policy [Policy Text Block]
Intangible Assets
Intangible Assets [Policy Text Block]
Intangible Assets Policy [Text Block]
Capitalized Financing Costs
Interest Capitalization, Policy [Policy Text Block]
Construction and Development in Progress
Construction In Progress [Policy Text Block]
Construction In Progress Policy [Text Block]
Depreciation and Amortization
Depreciation, Depletion, and Amortization [Policy Text Block]
Acquisitions and Goodwill
Acquisitions and Goodwill [Policy Text Block]
Acquisitions and Goodwill Policy [Text Block]
Long-Lived Asset Impairment
Asset Impairment [Policy Text Block]
Asset Impairment Policy [Text Block]
Costs of Arranging Debt Financing
Accounting Policy For Costs Of Arranging Debt Financing Policy [Policy Text Block]
Accounting Policy For Costs Of Arranging Debt Financing Policy [Text Block]
Comprehensive Income
Comprehensive Income, Policy [Policy Text Block]
Financial Assets and Liabilities
Fair Value Of Financial Assets And Liabilities [Policy Text Block]
Disclosure of accounting policy for fair value of financial assets and liabilities.
Derivative Instruments and Hedge Accounting
Derivatives, Methods of Accounting, Hedging Derivatives [Policy Text Block]
Employee Future Benefits
Pensions, Post-Retirement and Post Employment Benefits Policy [Policy Text Block]
Pensions, Post-Retirement and Post Employment Benefits Policy
Stock-Based Compensation
Share-based Payment Arrangement [Policy Text Block]
Loss Contingencies
Loss Contingencies [Policy Text Block]
Loss Contingencies [Policy Text Block]
Environmental Liabilities
Environmental Remediation Liabilities Policy [Policy Text Block]
Environmental Remediation Liabilities Policy [Policy Text Block]
Asset Retirement Obligations
Asset Retirement Obligation [Policy Text Block]
New Accounting Pronouncements
New Accounting Pronouncements, Policy [Policy Text Block]
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Subsidiary of Limited Liability Company or Limited Partnership [Table]
Schedule of Subsidiary of Limited Liability Company or Limited Partnership [Table]
Ownership [Axis]
Ownership [Axis]
Ownership [Domain]
Ownership [Domain]
B2M Limited Partnership [Member]
Bruce to Milton Limited Partnership [Member]
Bruce to Milton Limited Partnership [Member]
Niagara Reinforcement Limited Partnership [Member]
Niagara Reinforcement Limited Partnership [Member]
Niagara Reinforcement Limited Partnership [Member]
Counterparty Name [Axis]
Counterparty Name [Axis]
Counterparty Name [Domain]
Counterparty Name [Domain]
Province
Province Of Ontario [Member]
Province Of Ontario [Member]
Public Utilities, Regulatory Proceeding [Axis]
Public Utilities, Regulatory Proceeding [Axis]
Public Utilities, Regulatory Proceeding [Domain]
Public Utilities, Regulatory Proceeding [Domain]
2015 Approved Revenue Requirement [Member]
Two Thousand Fifteen Approved Revenue Requirement [Member]
Two Thousand Fifteen Approved Revenue Requirement [Member]
2016 Approved Revenue Requirement [Member]
Two Thousand Sixteen Approved Revenue Requirement [Member]
Two Thousand Sixteen Approved Revenue Requirement [Member]
2017 Approved Revenue Requirement [Member]
Two Thousand Seventeen Approved Revenue Requirement [Member]
Two Thousand Seventeen Approved Revenue Requirement [Member]
2018 Approved Revenue Requirement [Member]
Two Thousand Eighteen Approved Revenue Requirement [Member]
Two Thousand Eighteen Approved Revenue Requirement [Member]
2019 Approved Revenue Requirement [Member]
Two Thousand Nineteen Approved Revenue Requirement [Member]
Two Thousand Nineteen Approved Revenue Requirement [Member]
2020 Approved Revenue Requirement [Member]
Two Thousand Twenty Approved Revenue Requirement [Member]
Two Thousand Twenty Approved Revenue Requirement [Member]
2021 Approved Revenue Requirement [Member]
Two Thousand Twenty-One Approved Revenue Requirement [Member]
Two Thousand Twenty-One Approved Revenue Requirement [Member]
2022 Approved Revenue Requirement [Member]
Two Thousand Twenty-Two Approved Revenue Requirement [Member]
Two Thousand Twenty-Two Approved Revenue Requirement [Member]
Hydro One Remote Communities [Member]
Hydro One Remote Communities [Member]
Hydro One Remote Communities [Member]
Hydro One Sault Ste. Marie LP [Member]
Hydro One Sault Ste. Marie LP [Member]
Hydro One Sault Ste. Marie LP [Member]
Hydro One Networks [Member]
Hydro One Networks [Member]
Hydro One Networks [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership, percentage
Ownership, Percentage
Ownership, Percentage
Ownership interest in related party
Noncontrolling Interest, Ownership Percentage by Parent
Electrical transmission revenue index rate
Electrical Transmission Rate Application, Revenue Index
Electrical Transmission Rate Application, Revenue Index
Transmission revenue requirement
Electrical Transmission Revenue Requirement
Electrical transmission revenue requirement.
Deferred rebasing period
Deferred Rebasing Period
Deferred Rebasing Period
Revenue cap escalator
Revenue Cap Escalator
Revenue Cap Escalator
Distribution revenue requirement
Electrical Distribution Revenue Requirement.
Electrical distribution revenue requirement.
Electrical distribution, increased base rate
Electrical Distribution, Increased Base Rate
Electrical Distribution, Increased Base Rate
Significant Accounting Policies
Significant Accounting Policies [Text Block]
Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019
Operating Leases, Future Minimum Payments Due, Next Twelve Months
2020
Operating Leases, Future Minimum Payments, Due in Two Years
2021
Operating Leases, Future Minimum Payments, Due in Three Years
2022
Operating Leases, Future Minimum Payments, Due in Four Years
2023
Operating Leases, Future Minimum Payments, Due in Five Years
Thereafter
Operating Leases, Future Minimum Payments, Due Thereafter
Total undiscounted minimum lease payments
Operating Leases, Future Minimum Payments Due
Equity [Abstract]
Schedule of Stock by Class [Table]
Schedule of Stock by Class [Table]
Subsequent Event Type [Axis]
Subsequent Event Type [Axis]
Subsequent Event Type [Domain]
Subsequent Event Type [Domain]
Subsequent Event [Member]
Subsequent Event [Member]
Public
The General Public [Member]
The General Public [Member]
Plan Name [Axis]
Plan Name [Axis]
Plan Name [Domain]
Plan Name [Domain]
Long Term Incentive Plan [Member]
Long Term Incentive Plan [Member]
Long Term Incentive Plan [Member]
Share Grant Plans [Member]
Share Grant Plans [Member]
Share Grant Plans [Member]
Class of Stock [Line Items]
Class of Stock [Line Items]
Common shares – beginning
Common Stock, Shares, Outstanding
Common shares issued
Stock Issued During Period, Shares, New Issues
Common shares – ending
Number of shares exercised (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Value of common shares issued
Proceeds from Issuance of Common Stock
Regulatory Assets and Liabilities
Schedule of Regulatory Assets and Liabilities [Text Block]
Banking and Thrift, Interest [Abstract]
Interest on long-term debt
Interest Expense, Long-term Debt
Derecognition of deferred financing costs
Write off of Deferred Debt Issuance Cost
Unrealized loss (gain) on Foreign-Exchange Contract (Note 4)
Unrealized Gain (Loss) on Derivatives
Interest on short-term notes
Interest Expense, Short-term Borrowings
Interest on convertible debentures (Notes 4, 17)
Interest Costs Incurred
Other
Interest Expense, Other
Less: Interest capitalized on construction and development in progress
Interest Costs Capitalized Adjustment
Interest earned on cash and cash equivalents
Interest Income, Deposits with Financial Institutions
Net financing charges
Interest and Debt Expense
Pension Plans Postretirement And Other Employee Benefits [Table]
Pension Plans Postretirement And Other Employee Benefits [Table]
Pension Plans Postretirement And Other Employee Benefits [Table]
Defined Benefit Plan, Life Expectancy [Axis]
Defined Benefit Plan, Life Expectancy [Axis]
Defined Benefit Plan, Life Expectancy [Axis]
Defined Benefit Plan, Life Expectancy [Domain]
Defined Benefit Plan, Life Expectancy [Domain]
[Domain] for Defined Benefit Plan, Life Expectancy [Axis]
Life Expectancy At Age Sixty Five [Member]
Life Expectancy At Age Sixty Five [Member]
Life Expectancy At Age Sixty Five [Member]
Life Expectancy At Age Forty Five [Member]
Life Expectancy At Age Forty Five [Member]
Life Expectancy At Age Forty Five [Member]
Title of Individual [Axis]
Title of Individual [Axis]
Title of Individual [Domain]
Title of Individual [Domain]
Male [Member]
Male [Member]
Male [Member]
Female [Member]
Female [Member]
Female [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Approximate life expectancy (in years) at particular age
Approximate Life Expectancy In years At Particular Age
Approximate life expectancy at particular age.
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets
Schedule of Finite-Lived Intangible Assets [Table Text Block]
Property, Plant and Equipment [Abstract]
Depreciation of property, plant and equipment
Depreciation
Amortization of intangible assets
Amortization of Intangible Assets
Amortization of regulatory assets
Amortization of Regulatory Asset
Depreciation and amortization
Depreciation, Depletion and Amortization
Asset removal costs
Amortization Of Capitalized Asset Retirement Obligation Costs
The amortization of the asset retirement obligation costs that got capitalized.
Total depreciation and amortization
Depreciation, Depletion and Amortization, Nonproduction
Share-based Payment Arrangement [Abstract]
Exercise price (in dollars per share)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price
Grant date fair value per option (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Grant Date Intrinsic Value
Expected dividend yield
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate
Expected volatility
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate
Risk-free interest rate
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate
Expected option term
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share grants outstanding, beginning (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number
Shares granted (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross
Shares exercised (in shares)
Shares forfeited (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period
Share grants outstanding, ending (in shares)
Weighted-average exercise price, granted (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value
Weighted-average exercise price, forfeited (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value
Weighted-average price, outstanding (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Number of options vested with a modified fair value (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares
Fair value of options forfeited (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Fair Value
Number of modified fair value options (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Modified Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Modified Fair Value
Aggregate intrinsic value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value
Contractual term
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term
Aggregate intrinsic value of options exercised
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value
Unrecognized compensation expense
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount
Payables and Accruals [Abstract]
Accounts payable
Accounts Payable, Current
Accrued liabilities
Accrued Liabilities, Current
Accrued interest
Interest Payable, Current
Regulatory liabilities (Note 12)
Regulatory Liability, Current
Lease obligations (Note 23)
Operating Lease, Liability, Current
Total
Accounts Payable and Other Accrued Liabilities, Current
Effect of a 1% increase in health care cost trends
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components
Effect of a 1% decrease in health care cost trends
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components
Other Liabilities Disclosure [Abstract]
Other Long-Term Liabilities
Other Liabilities Disclosure [Text Block]
Noncontrolling Interest [Abstract]
Noncontrolling Interest [Table]
Noncontrolling Interest [Table]
Noncontrolling Interest [Line Items]
Noncontrolling Interest [Line Items]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Noncontrolling interest - beginning balance, temporary equity
Redeemable Noncontrolling Interest, Equity, Carrying Amount
Contributions from sale of noncontrolling interest, temporary equity
Temporary Equity Contribution During Period Value
Temporary Equity Contribution During Period Value
Distributions to noncontrolling interest, temporary equity
Temporary Equity Distribution During Period Value
Temporary Equity Distribution During Period Value
Net income attributable to noncontrolling interest, temporary equity
Temporary Equity, Net Income
Noncontrolling interest - ending balance, temporary equity
Noncontrolling interest - beginning balance, equity
Stockholders' Equity Attributable to Noncontrolling Interest
Contributions from sale of noncontrolling interest, equity
Noncontrolling Interest, Increase from Sale of Parent Equity Interest
Distributions to noncontrolling interest, equity
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders
Net income attributable to noncontrolling interest, equity
Noncontrolling Interest In Net Income Loss Equity
Amount of income (loss) attributable to noncontrolling Interest equity portion.
Noncontrolling interest - ending balance, equity
Noncontrolling interest - beginning balance
Minority Interest And Redeemable Noncontrolling Interest Equity And Temporary Equity
Minority Interest And Redeemable Noncontrolling Interest Equity And Temporary Equity
Contributions from sale of noncontrolling interest
Minority Interest Temporary Equity And Equity Increase From Sales Of Noncontrolling Interest
Minority Interest Temporary Equity And Equity Increase From Sales Of Noncontrolling Interest
Distributions to noncontrolling interest
Minority Interest Temporary Equity And Equity Decrease From Distributions To Noncontrolling Interest Holders
Minority interest temporary equity and equity decrease from distributions to noncontrolling interest holders.
Net income attributable to noncontrolling interest
Net Income (Loss) Attributable to Noncontrolling Interest
Noncontrolling interest - ending balance
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Directors' Deferred Share Units Plan [Member]
Directors' Deferred Share Units Plan [Member]
Directors' Deferred Share Units Plan [Member]
Management Deferred Share Units Plan [Member]
Management Deferred Share Units Plan [Member]
Management Deferred Share Units Plan [Member]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain]
Deferred Share Units [Member]
Deferred Share Unit [Member]
Deferred Share Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
DSUs outstanding - January 1 (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number
DSUs granted (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted
DSUs settled (in shares)
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Settled In Period
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Settled In Period
DSUs paid (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised
DSUs outstanding - December 31 (in shares)
Environmental Remediation Obligations [Abstract]
Environmental Liabilities [Table]
Environmental Liabilities [Table]
Environmental Liabilities [Table]
Environmental Remediation Site [Axis]
Environmental Remediation Site [Axis]
Environmental Remediation Site [Domain]
Environmental Remediation Site [Domain]
PCB [Member]
PCB [Member]
PCB [Member]
Land Assessment and Remediation [Member]
Land Assessment And Remediation [Member]
Land Assessment And Remediation [Member]
Environmental Liabilities [Line Items]
Environmental Liabilities [Line Items]
Environmental Liabilities [Line Items]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies [Roll Forward]
Environmental liabilities - beginning
Environmental Liabilities
Environmental Liabilities
Interest accretion
Interest Accretion
Interest accretion.
Expenditures
Environmental Expense and Liabilities
Revaluation adjustment
Increase Decrease In Revaluation Of Environmental Liabilities
Increase decrease in revaluation of environmental liabilities.
Environmental liabilities - ending
Less: current portion
Environmental Liabilities Current Portion
Environmental liabilities current portion.
Environmental liabilities non current portion
Environment Liabilities Non Current
Environment liabilities non current.
Business Combinations [Abstract]
Business Combinations
Business Combination Disclosure [Text Block]
Statement of Financial Position [Abstract]
Long-term debt measured at fair value
Fair Value Of Hedged Debt
Fair value of hedged debt.
Pension Benefits [Member]
Pension Plan [Member]
Change in projected benefit obligation
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, beginning of year
Defined Benefit Plan, Benefit Obligation
Current service cost
Defined Benefit Plan, Service Cost
Employee contributions
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant
Interest cost
Defined Benefit Plan, Interest Cost
Benefit paid
Defined Benefit Plan, Benefit Obligation, Benefits Paid
Net actuarial loss (gain)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)
Recognition of prior service
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)
Net transfers
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Other Change
Projected benefit obligation, end of year
Change in plan assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year
Defined Benefit Plan, Plan Assets, Amount
Actual return on plan assets
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)
Benefits paid
Defined Benefit Plan, Plan Assets, Benefits Paid
Employer contributions
Defined Benefit Plan, Plan Assets, Contributions by Employer
Employee contributions
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant
Administrative expenses
Defined Benefit Plan, Plan Assets, Administration Expense
Fair value of plan assets, end of year
Unfunded status
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Other long-term assets (Note 13)
Operating Lease, Right-of-Use Asset
Accounts payable and other current liabilities (Note 14)
Other long-term liabilities (Note 15)
Operating Lease, Liability, Noncurrent
Related Party Transactions [Abstract]
Related Party Transactions
Related Party Transactions Disclosure [Text Block]
Schedule of Defined Benefit Plans Disclosures [Table]
Schedule of Defined Benefit Plans Disclosures [Table]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Disclosure [Line Items]
Change in Projected Benefit Obligation and Change in Plan Assets
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan [Table Text Block]
Schedule of Benefit Obligations and Plan Assets
Schedule Of Balance Sheet Presentation Of Net Benefit Liabilities [Table Text Block]
Tabular disclosure of pension and post-retirement and post-employment benefits based on balance sheet presentation.
Schedule of Projected Benefit Obligation (PBO), Accumulated Benefit Obligation (ABO) and Fair Value of Plan Assets
Schedule of Accumulated and Projected Benefit Obligations [Table Text Block]
Components of Net Periodic Benefit Costs
Schedule of Net Benefit Costs [Table Text Block]
Schedule of Weighted Average Assumptions Used to Determine Benefit Obligations
Schedule Of Weighted Average Assumptions Used To Determine Benefit Obligations [Table Text Block]
Schedule Of Weighted Average Assumptions Used To Determine Benefit Obligations
Schedule of Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Schedule Of Weighted Average Assumptions Used In Calculating Net Periodic Benefit Costs [Table Text Block]
Schedule Of Weighted Average Assumptions Used In Calculating Net Periodic Benefit Costs
Schedule of Effect of One Percent Change in Health Care Cost Trends on Projected Benefit Obligation
Schedule Of Effect Of One percent Change In Health Care Cost Trends On Projected Benefit Obligation [Table Text Block]
Schedule Of Effect Of One percent Change In Health Care Cost Trends On Projected Benefit Obligation
Schedule of Effect of One Percent Change in Health Care Cost Trends on Service Cost and Interest Cost
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]
Approximate Life Expectancies Used to Determine Projected Benefit Obligations for Pension, Post-Retirement and Post-Employment Plans
Life Expectancies Used To Determine Projected Benefit Obligations For Pension And Post Employment Plans [Table Text Block]
Life Expectancies Used To Determine Projected Benefit Obligations For Pension And Post Employment Plans [Table Text Block]
Schedule of Estimated Future Benefit Payments
Schedule of Expected Benefit Payments [Table Text Block]
Schedule of Actuarial Gains and Losses and Prior Service Costs Recorded Within Regulatory Assets
Schedule Of Actuarial Gains And Losses And Prior Service Costs Recorded Within Regulatory Assets [Table Text Block]
Schedule Of Actuarial Gains And Losses And Prior Service Costs Recorded Within Regulatory Assets [Table Text Block]
Components of Regulatory Assets That Have Not Been Recognized as Components of Net Periodic Benefit Costs
Components Of Regulatory Assets That Have Not Been Recognized As Components Of Net Periodic Benefit Costs [Table Text Block]
Components Of Regulatory Assets That Have Not Been Recognized As Components Of Net Periodic Benefit Costs Table [Text Block]
Components of Regulatory Assets Expected to be Amortized as Components of Net Periodic Benefit Costs
Components Of Regulatory Assets To Be Amortized Net Periodic Benefit Costs [Table Text Block]
Components Of Regulatory Assets To Be Amortized Net Periodic Benefit Costs Table [Text Block]
Schedule of Pension Plan Target Asset and Weighted Average Asset Allocations
Schedule Of Pension Plan Target Asset And Weighted Average Asset Allocations [Table Text Block]
Schedule Of Pension Plan Target Asset And Weighted Average Asset Allocations
Pension Plan Assets Measured and Recorded at Fair Value on Recurring Basis
Schedule of Allocation of Plan Assets [Table Text Block]
Changes in Fair Value of Financial Instruments Classified in Level 3
Schedule of Changes in Fair Value of Plan Assets [Table Text Block]
Award Type [Axis]
Award Type [Axis]
Award Type [Domain]
Award Type [Domain]
Performance Share Units [Member]
Performance Share Units [Member]
Performance share units.
Restricted Stock Units (RSUs) [Member]
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Units outstanding - beginning (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number
Granted (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Vested and issued (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period
Forfeited (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Settled (in shares)
Units outstanding - ending (in shares)
Number of units outstanding, potentially unsettled (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Units Potentially Settled
Share-based Compensation Arrangement by Share-based Payment Award, Units Potentially Settled
Liability recorded for potentially unsettled shares
Deferred Compensation Share-based Arrangements, Liability, Current
Valuation allowance in respect of capital property
Deferred Tax Assets, Valuation Allowance
Schedule Of Convertible Debentures
Convertible Debt [Table Text Block]
Schedule Of Weighted Average Assumptions Determining Pension Plan And Other Post retirement Benefit Plan [Table]
Schedule Of Weighted Average Assumptions Determining Pension Plan And Other Post retirement Benefit Plan [Table]
Schedule Of Weighted Average Assumptions Determining Pension Plan And Other Post retirement Benefit Plan [Table]
Schedule Of Weighted Average Assumption Determining Pension Plan And Other Post retirement Benefit Plan [Line Items]
Schedule Of Weighted Average Assumption Determining Pension Plan And Other Post retirement Benefit Plan [Line Items]
Schedule Of Weighted Average Assumption Determining Pension Plan And Other Post retirement Benefit Plan [Line Items]
Weighted average expected rate of return on plan assets
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Return On Plan Assets
Defined benefit plan assumptions used calculating net periodic benefit cost rate of return on plan assets.
Weighted average discount rate
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate
Rate of compensation scale escalation (long-term)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase
Rate of cost of living increase
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Cost Of Living Increase
Defined benefit plan assumptions used calculating net periodic benefit cost rate of cost of living increase.
Average remaining service life of employees (years)
Defined Benefit Plan Assumptions Used In Calculations Average Remaining Service Period
Defined benefit plan assumptions used in calculations average remaining service period.
Rate of increase in health care cost trends
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Health Care Cost Trend Rate
Defined benefit plan assumptions used calculating net periodic benefit cost health care cost trend rate.
Assumed health care cost trend, percentage
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year
Health care cost trend rate
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate
Schedule of Other Long-Term Liabilities
Other Noncurrent Liabilities [Table Text Block]
Capital Management
Capital Structure Disclosure [Text Block]
Capital Structure Disclosure [Text Block]
Financing charges related to intangible assets under development
Financing Charges Related To Intangible Assets Under Development
Financing Charges Related To Intangible Assets Under Development
Amortization expense for intangible assets, 2020
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months
Amortization expense for intangible assets, 2021
Finite-Lived Intangible Assets, Amortization Expense, Year Two
Amortization expense for intangible assets, 2022
Finite-Lived Intangible Assets, Amortization Expense, Year Three
Amortization expense for intangible assets, 2023
Finite-Lived Intangible Assets, Amortization Expense, Year Four
Amortization expense for intangible assets, 2024
Finite-Lived Intangible Assets, Amortization Expense, Year Five
Schedule of Regulatory Assets and Liabilities
Schedule Of Regulatory Assets And Liabilities [Table Text Block]
Schedule Of Regulatory Assets And Liabilities [Table Text Block]
Schedule of Business Acquisitions, by Acquisition [Table]
Schedule of Business Acquisitions, by Acquisition [Table]
Six Nations Of The Grand River Development Corporation [Member]
Six Nations Of The Grand River Development Corporation [Member]
Six Nations Of The Grand River Development Corporation [Member]
Mississaugas Of The Credit First Nation [Member]
Mississaugas Of The Credit First Nation [Member]
Mississaugas Of The Credit First Nation [Member]
First Nations [Member]
First Nations [Member]
First Nations [Member]
Financial Instrument [Axis]
Financial Instrument [Axis]
Financial Instruments [Domain]
Financial Instruments [Domain]
Debt [Member]
Debt [Member]
Equity [Member]
Equity [Member]
Debt Instrument [Axis]
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
Equity Bridge [Member]
Equity Bridge [Member]
Equity Bridge [Member]
Debt Bridge [Member]
Debt Bridge [Member]
Debt Bridge [Member]
Line of Credit [Member]
Line of Credit [Member]
Business Acquisition [Axis]
Business Acquisition [Axis]
Business Acquisition, Acquiree [Domain]
Business Acquisition, Acquiree [Domain]
Six Nations Of The Grand River Development Corporation And Mississaugas Of The Credit First Nation [Member]
Six Nations Of The Grand River Development Corporation And Mississaugas Of The Credit First Nation [Member]
Six Nations Of The Grand River Development Corporation And Mississaugas Of The Credit First Nation [Member]
Avista Corporation [Member]
Avista Corporation [Member]
Avista Corporation [Member]
Orillia Power Distribution Corporation [Member]
Orillia Power Distribution Corporation [Member]
Orillia Power Distribution Corporation.
Peterborough Distribution Inc. [Member]
Peterborough Distribution Inc. [Member]
Peterborough Distribution Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition [Line Items]
Business combination percentage transferred
Business Combination Consideration Transferred Percentage
Business combination consideration transferred percentage.
Consideration transferred
Business Combination, Consideration Transferred
Percentage of common shares acquired
Business Acquisition, Percentage of Voting Interests Acquired
Additional equity interest available for purchase
Business Acquisition, Option To Purchase Additional Voting Interests Percentage
Business Acquisition, Option To Purchase Additional Voting Interests Percentage
Termination fee
Business Combination, Termination Fee
Business Combination, Termination Fee
Termination of facility
Line Of Credit Facility, Termination Of Facility
Line Of Credit Facility, Termination Of Facility
Repayments of credit facility
Repayments of Long-term Lines of Credit
Repayments of convertible debt
Repayments of Convertible Debt
Payments for interest
Payments For Interest
Payments For Interest
Operation, maintenance and administration
Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses
Financing charges
Purchase price of acquisition
Business Acquisition Purchase Price
Business Acquisition Purchase Price
Business acquisition, consideration outstanding indebtedness
Business Combination, Consideration Transferred, Liabilities Incurred
Conversion ratio
Debt Instrument, Convertible, Conversion Ratio
Schedule of Accounts Payable and Other Current Liabilities
Schedule of Accounts Payable and Accrued Liabilities [Table Text Block]
Other Current Assets
Other Current Assets [Text Block]
Accounting Policies [Table]
Accounting Policies [Table]
Accounting Policies [Table]
Adjustments for New Accounting Pronouncements [Axis]
Adjustments for New Accounting Pronouncements [Axis]
Type of Adoption [Domain]
Type of Adoption [Domain]
Accounting Standards Update 2016-02 [Member]
Accounting Standards Update 2016-02 [Member]
Accounting Policies [Line Items]
Accounting Policies [Line Items]
Accounting Policies [Line Items]
Short-term investments original maturity
Short Term Investment Original Maturity Term Maximum
Cash equivalent short term investment original maturity term maximum.
Asset impairment charges
Asset Impairment Charges
Embedded derivatives
Embedded Derivative, Fair Value of Embedded Derivative, Net
Operating lease, right-of-use asset
Operating lease liability
Operating Lease, Liability
Schedule of Related Party Transactions, by Related Party [Table]
Schedule of Related Party Transactions, by Related Party [Table]
Other Commitments [Axis]
Other Commitments [Axis]
Other Commitments [Domain]
Other Commitments [Domain]
Guarantees [Member]
Guarantees [Member]
Product and Service [Axis]
Product and Service [Axis]
Product and Service [Domain]
Product and Service [Domain]
Transmission [Member]
Electric Transmission [Member]
Electricity, US Regulated [Member]
Electricity, US Regulated [Member]
Distribution [Member]
Electric Distribution [Member]
Related Party Transaction [Axis]
Related Party Transaction [Axis]
Related Party Transaction [Domain]
Related Party Transaction [Domain]
OCN LP [Member]
OCN LP [Member]
OCN LP [Member]
Amounts Related To Electricity Rebates [Member]
Amounts Related To Electricity Rebates [Member]
Amounts Related To Electricity Rebates [Member]
Related Party [Axis]
Related Party [Axis]
Related Party [Domain]
Related Party [Domain]
The Province [Member]
Affiliated Entity [Member]
IESO [Member]
Independent Electricity System Operator [Member]
Independent Electricity System Operator [Member]
OPG [Member]
Ontario Power Generation [Member]
Ontario Power Generation [Member]
OEFC [Member]
Ontario Electricity Financial Corporation [Member]
Ontario Electricity Financial Corporation [Member]
OEB [Member]
Ontario Energy Board [Member]
Ontario Energy Board [Member]
Ontario Charging Network [Member]
Ontario Charging Network [Member]
Ontario Charging Network [Member]
Public Utility [Axis]
Public Utility [Axis]
Utility Plant [Domain]
Utility Plant [Domain]
Related Party Transaction [Line Items]
Related Party Transaction [Line Items]
Dividends
Dividends
Purchased power costs
Cost of Goods and Services Sold
Revenues for transmission services
Revenue from Contract with Customer, Including Assessed Tax
Related party transaction amount
Related Party Transaction, Amounts of Transaction
Funding received related to CDM programs
Related party funding received for program costs, incentives and management fees
Related party funding received for program costs, incentives and management fees
Revenues related to provision of services and supply of electricity
Related Party Transaction, Other Revenues from Transactions with Related Party
Costs related to the purchase of services
Related Party Transaction, Expenses from Transactions with Related Party
OEB fees
Related Party Reimbursement Expenses
Related party reimbursement expenses.
Other commitments due
Other Commitment, Due in Next Twelve Months
Subsequent Events [Abstract]
Subsequent Event [Table]
Subsequent Event [Table]
Subsequent Event [Line Items]
Subsequent Event [Line Items]
Preferred share dividends
Dividends, Preferred Stock
Common share dividends
Dividends, Common Stock
Dividends per common share declared (in dollars per share)
Common Stock, Dividends, Per Share, Declared
Business combination assets transferred
Interest in equity portion
Ownership percentage
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners
Proceeds from stock options exercised
Proceeds from Stock Options Exercised
Subsequent Events
Subsequent Events [Text Block]
Property, Plant and Equipment [Table]
Property, Plant and Equipment [Table]
Communication [Member]
Communications [Member]
Communications [Member]
Administration and Service [Member]
Administrative Support Services [Member]
Administrative Support Services [Member]
Easements [Member]
Land Easements [Member]
Land Easements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment
Property, Plant and Equipment, Gross
Accumulated Depreciation
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment
Construction in Progress
Construction in Progress, Gross
Property, plant, and equipment, total
Property, Plant and Equipment, Net
Undiscounted environmental liabilities
Environmental Liabilities Undiscounted Basis
Environmental liabilities undiscounted basis.
Less: discounting environmental liabilities to present value
Accrued Discount Liability
Accrued discount liability.
Discounted environmental liabilities
Environmental Liabilities Discounted Basis
Environmental liabilities discounted basis.
Right-of-use asset
Other
Other Assets, Miscellaneous, Noncurrent
Total other assets
Other Assets, Noncurrent
Schedule of Property, Plant and Equipment
Property, Plant and Equipment [Table Text Block]
Share Capital
Stockholders' Equity Note Disclosure [Text Block]
Receivables [Abstract]
Schedule of Accounts Receivable
Schedule Of Accounts Receivable Table [Table Text Block]
Schedule Of Accounts Receivable Table [Table Text Block]
Schedule of Allowance for Doubtful Accounts
Schedule Of Allowance For Doubtful Accounts [Table Text Block]
Tabular disclosure of the amount of bad debt provision charged against earnings and the amounts of accounts receivable written off.
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments and Risk Management
Fair Value Disclosures [Text Block]
Schedule of Financing Charges
Interest Income and Interest Expense Disclosure [Table Text Block]
Supplemental Cash Flow Information [Abstract]
Schedule of Consolidated Statement of Cash Flows
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]
Income Statement [Abstract]
Statement [Table]
Statement [Table]
Related Party [Member]
Related Party [Member]
Related Party [Member]
Statement [Line Items]
Statement [Line Items]
Revenues
Reconciliation between Statutory and Effective Tax Rates
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Major Components of Income Tax Expense
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]
Schedule of Deferred Income Tax Assets and Liabilities
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
Major Categories of Net Deferred Income Tax Assets
Net Deferred Income Tax Assets And Liabilities Table [Text Block]
Net deferred income tax assets and liabilities.
Non Capital Losses Carried Forward to Reduce Future Period Taxable Income
Non Capital Losses Carried Forward By Year Of Expiry [Table Text Block]
Non capital losses carried forward by year of expiry.
Commitments and Contingencies Disclosure [Abstract]
Summary of Commitments Under Leases, Outsourcing and Other Agreements Due
Contractual Obligation, Fiscal Year Maturity [Table Text Block]
Summary of Other Commitments
Other Commitments [Table Text Block]
Post-retirement and post-employment benefit liability (Note 20)
Postretirement And Postemployment Benefit Plans Liabilities Non Current
Postretirement and postemployment benefit plans liabilities non current.
Pension benefit liability (Note 20)
Liability, Defined Benefit Pension Plan, Noncurrent
Environmental liabilities (Note 21)
Accrued Environmental Loss Contingencies, Noncurrent
Lease obligations (Note 23)
Long-term accounts payable
Due to Related Parties, Noncurrent
Asset retirement obligations (Note 22)
Asset Retirement Obligation
Other liabilities
Other Liabilities, Miscellaneous, Noncurrent
Other Liabilities, Miscellaneous, Noncurrent
Other long-term liabilities
Other Liabilities, Noncurrent
PWU Share Grant Plan [Member]
PWU Share Grant Plan [Member]
PWU Share Grant Plan [Member]
Shares vested and issued (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average price, outstanding, beginning (in dollars per share)
Weighted-average exercise price, vested and issued (in dollars per share)
Weighted-average price, outstanding, ending (in dollars per share)
Property Plant And Equipment Estimated Useful Lives [Table]
Property Plant And Equipment Estimated Useful Lives [Table]
Property Plant And Equipment Estimated Useful Lives [Table]
Administration and Service [Member]
Administrative And Support Services And Others [Member]
Administrative And Support Services And Others [Member]
Statistical Measurement [Axis]
Statistical Measurement [Axis]
Statistical Measurement [Domain]
Statistical Measurement [Domain]
Minimum [Member]
Minimum [Member]
Maximum [Member]
Maximum [Member]
Property Plant And Equipment Estimated Useful Lives [Line Items]
Property Plant And Equipment Estimated Useful Lives [Line Items]
Property Plant And Equipment Estimated Useful Lives [Line Items]
Average service life, property, plant and equipment
Property, Plant and Equipment, Useful Life
Average service life, property, plant and equipment
Long Lived Assets And Intangible Assets Useful Life
Long Lived Assets And Intangible Assets Useful Life
Average service life, intangible assets
Finite-Lived Intangible Asset, Useful Life
Annual rate of depreciation and amortization, property, plant and equipment
Annual Depreciation and Amortization Rate Range
Annual Depreciation and Amortization Rate Range
Annual average rate of depreciation and amortization, property, plant and equipment
Average Depreciation and Amortization Rate
Average Depreciation and Amortization Rate
Annual average rate of amortization, intangible assets
Average Amortization Rate On Intangible Assets
Average amortization rate on intangible assets.
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-term Debt Instruments [Table]
Long-term Debt, Type [Axis]
Long-term Debt, Type [Axis]
Long-term Debt, Type [Domain]
Long-term Debt, Type [Domain]
Convertible Debt [Member]
Convertible Debt [Member]
Debt Instrument [Line Items]
Debt Instrument [Line Items]
Debt [Roll Forward]
Debt [Roll Forward]
Debt [Roll Forward]
Carrying value - beginning
Convertible Debt, Noncurrent
Amortization of deferred financing costs
Amortization of Debt Issuance Costs
Derecognition of deferred financing costs (Note 4)
Redemption (Note 4)
Proceeds from Convertible Debt
Carrying value - ending
Long-term debt
Debt Instrument, Face Amount
Accounts Payable and Other Current Liabilities
Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block]
Schedule of Depreciation and Amortization
Schedule Of Depreciation And Amortization [Table Text Block]
Schedule Of Depreciation And Amortization
Post-Retirement and Post-Employment Benefits [Member]
Postretirement Benefit Costs [Member]
Current service cost
Defined Benefit Plan Service Cost Net Of Employee Contribution
Defined benefit plan service cost net of employee contribution.
Expected return on plan assets, net of expenses
Defined Benefit Plan, Expected Return (Loss) on Plan Assets
Amortization of actuarial losses
Defined Benefit Plan, Amortization of Gain (Loss)
Net periodic benefit costs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Charged to results of operations
Net Periodic Benefit Cost Charged To Operations
Net periodic benefit cost charged to operations.
Pension costs
Pension Costs Attributed To Labour Employer Contribution
Pension costs attributed to labour employer contribution.
Pension costs charged to operations
Pension Costs Charged To Operations
Pension costs charged to operations.
Pension costs capitalized
Pension Costs Capitalized
Pension costs capitalized.
Other Long-Term Assets
Other Non-Current Assets [Text Block]
Other Non-Current Assets [Text Block]
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Table]
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Table]
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Table]
Hedging Designation [Axis]
Hedging Designation [Axis]
Hedging Designation [Domain]
Hedging Designation [Domain]
Designated as Hedging Instrument [Member]
Designated as Hedging Instrument [Member]
$300 million of MTN Series 39 notes [Member]
Three Hundred Million Of Medium Term Note Series Thirty Nine Notes [Member]
Three Hundred Million Of Medium Term Note Series Thirty Nine Notes [Member]
Derivative Instrument [Axis]
Derivative Instrument [Axis]
Derivative Contract [Domain]
Derivative Contract [Domain]
Interest Rate Swap [Member]
Interest Rate Swap [Member]
Foreign Exchange Contract [Member]
Foreign Exchange Contract [Member]
1.62% Series 33 Notes Due 2020 [Member]
One Point Six Two Percent Thirty Three Notes Due Two Thousand Twenty [Member]
One Point Six Two Percent Thirty Three Notes Due Two Thousand Twenty [Member]
1.48% Series 37 Notes Due 2019 [Member]
One Point Four Eight Percent Series Thirty Seven Notes Due Two Thousand Nineteen [Member]
One point four eight percent series thirty seven notes due two thousand nineteen.
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Line Items]
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Line Items]
Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments [Line Items]
Fixed-to-floating interest-rate swap
Fixed To Floating Interest Rate Swaps
Fixed To Floating Interest Rate Swaps
Fixed-to-floating interest-rate swap, term
Fixed To Floating Interest Rate Swaps, Term
Fixed To Floating Interest Rate Swaps, Term
Fair value hedge exposure
Percentage Of Fair Value Hedge Exposure
Percentage Of Fair Value Hedge Exposure
Conversion of debt
Debt Conversion, Original Debt, Amount
Notional value
Derivative, Notional Amount
Forward exchange rate
Derivative, Forward Exchange Rate
Unrealized gains reversed in financing charges
Schedule of Common Stock Outstanding Roll Forward
Schedule of Common Stock Outstanding Roll Forward [Table Text Block]
Defined Benefit Plan, Plan Assets, Category [Axis]
Defined Benefit Plan, Plan Assets, Category [Axis]
Defined Benefit Plan, Plan Assets, Category [Domain]
Defined Benefit Plan, Plan Assets, Category [Domain]
Equity Securities [Member]
Defined Benefit Plan, Equity Securities [Member]
Debt Securities [Member]
Defined Benefit Plan, Debt Security [Member]
Other Plan Assets [Member]
Other Plan Assets [Member]
Other Plan Assets [Member]
Target Allocation
Pension Plan Asset Percentage
Pension plan asset percentage.
Pension Plan Assets
Target Allocation Percentage
Target allocation percentage.
PBO
ABO
Defined Benefit Plan, Accumulated Benefit Obligation
Fair value of plan assets
Market Risk Credit Risk And Liquidity Risk [Table]
Market Risk Credit Risk And Liquidity Risk [Table]
Market Risk Credit Risk And Liquidity Risk [Table]
Equity Components [Axis]
Equity Components [Axis]
Equity Component [Domain]
Equity Component [Domain]
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Hydro One Holdings Limited [Member]
Hydro One Holdings Limited [Member]
Hydro One Holdings Limited [Member]
Financial Asset, Period Past Due [Axis]
Financial Asset, Period Past Due [Axis]
Financial Asset, Period Past Due [Domain]
Financial Asset, Period Past Due [Domain]
Aged More Than 60 Days [Member]
Financing Receivables Equal To Greater Than 60 Days Past Due [Member]
Financing Receivables Equal To Greater Than 60 Days Past Due [Member]
Market Risk, Credit Risk And Liquidity Risk [Line Items]
Market Risk, Credit Risk And Liquidity Risk [Line Items]
Market Risk, Credit Risk And Liquidity Risk [Line Items]
Unrealized gain on cash flow hedges, net of tax
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax
Accumulated other comprehensive income related to cash flow hedges
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest
Maximum term of hedges
Derivative, Term of Contract
Amounts reclassified to results of operations
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax
Provision for bad debts
Accounts Receivable, Allowance for Credit Loss, Current
Account receivable, percentage
Account Receivable Net Percentage
Account Receivable Net Percentage
Account receivable, period
Accounts Receivable Collection Period
Accounts Receivable Collection Period
Maximum public offering amount
Maximum Public Offering Amount
Maximum Public Offering Amount
Public offering period
Public Offering Period
Public Offering Period
Schedule of Other Non-Current Assets
Schedule of Other Non-Current Assets [Table Text Block]
Schedule of Other Non-Current Assets [Table Text Block]
Fair Value Of Financial Instruments [Table]
Fair Value Of Financial Instruments [Table]
Fair Value Of Financial Instruments [Table]
Fair Value Hierarchy and NAV [Axis]
Fair Value Hierarchy and NAV [Axis]
Fair Value Hierarchy and NAV [Domain]
Fair Value Hierarchy and NAV [Domain]
Level 3 [Member]
Fair Value, Inputs, Level 3 [Member]
Fair Value Of Financial Instruments [Line Items]
Fair Value Of Financial Instruments [Line Items]
Fair Value Of Financial Instruments [Line Items]
Realized and unrealized gains (losses)
Defined Benefit Plan Fair Value Of Plan Assets Realized And Unrealized Gains
Defined benefit plan fair value of plan assets realized and unrealized gains.
Purchases
Defined Benefit Plan Fair Value Of Plan Assets Purchases
Defined benefit plan fair value of plan assets purchases.
Sales and disbursements
Defined Benefit Plan Fair Value Of Plan Assets Sales
Defined benefit plan fair value of plan assets sales.
Type Of Benefit Obligation [Axis]
Type Of Benefit Obligation [Axis]
Type Of Benefit Obligation [Axis]
Type Of Benefit Obligation [Domain]
Type Of Benefit Obligation [Domain]
[Domain] for Type Of Benefit Obligation [Axis]
ABO [Member]
Accumulated Benefit Obligation [Member]
Accumulated Benefit Obligation [Member]
PBO [Member]
Projected Benefit Obligation [Member]
Projected Benefit Obligation [Member]
Province Of Ontario [Member]
Majority Shareholder [Member]
Investment Type [Axis]
Investment Type [Axis]
Investments [Domain]
Investments [Domain]
Corporate Bond Securities [Member]
Corporate Bond Securities [Member]
Retirement Plan Name [Axis]
Retirement Plan Name [Axis]
Retirement Plan Name [Domain]
Retirement Plan Name [Domain]
Option One [Member]
Option One [Member]
Option One [Member]
Option Two [Member]
Option Two [Member]
Option Two [Member]
Option Three [Member]
Option Three [Member]
Option Three [Member]
Percentage of employer matching contribution
Defined Contribution Plan, Employer Matching Contribution, Percent of Match
Contributions by company to the plan
Defined Contribution Plan Employer Contribution Amount
Amount of contributions made by an employer to a defined contribution plan.
Pension plan average pensionable earnings
Defined Benefit Plan Average Pensionable Earnings
Defined benefit plan average pensionable earnings.
New pension plan average pensionable earnings
Defined Benefit Plan New Average Pensionable Earnings
Defined benefit plan new average pensionable earnings.
Annual pension plan contributions
Estimated annual pension plan contributions for 2020
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year
Estimated annual pension plan contributions for 2021
Defined Benefit Plan, Expected Future Benefit Payment, Year Two
Estimated annual pension plan contributions for 2022
Defined Benefit Plan, Expected Future Benefit Payment, Year Three
Estimated annual pension plan contributions for 2023
Defined Benefit Plan, Expected Future Benefit Payment, Year Four
Estimated annual pension plan contributions for 2024
Defined Benefit Plan, Expected Future Benefit Payment, Year Five
Estimated annual pension plan contributions thereafter
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter
Funded percentage
Defined Benefit Plan, Funded Percentage
Pension plan
Defined Benefit Plan, Plan Assets, Employer, Related Party, Amount
Gain (loss) on derivative. net
Derivative, Gain (Loss) on Derivative, Net
Statement of Stockholders' Equity [Abstract]
Common Shares [Member]
Common Stock [Member]
Preferred Stock [Member]
Preferred Stock [Member]
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
Retained Earnings [Member]
Retained Earnings [Member]
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent [Member]
Hydro One [Member]
Parent [Member]
Non-controlling Interest [Member]
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance
Net income
Net Income Loss Net Of Adjustments To Noncontrolling Interest Subject To Redemption
Net income loss net of adjustments to noncontrolling interest subject to redemption.
Other comprehensive income (loss)
Other Comprehensive Income (Loss), Net of Tax
Distributions to noncontrolling interest
Contributions from sale of noncontrolling interest (Note 4)
Dividends on preferred shares
Dividends on common shares
Common shares issued
Stock Issued During Period, Value, New Issues
Stock-based compensation (Note 27)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition
Ending balance
Property, Plant and Equipment
Property, Plant and Equipment Disclosure [Text Block]
Capital Units by Class [Axis]
Capital Units by Class [Axis]
Capital Unit, Class [Domain]
Capital Unit, Class [Domain]
Class A Units [Member]
Capital Unit, Class A [Member]
Class B Units [Member]
Capital Unit, Class B [Member]
Saugeen Ojibway Nation (SON) [Member]
Saugeen Ojibway Nation [Member]
Saugeen Ojibway Nation [Member]
Business acquisition, consideration paid
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable
Capital units in initial investment
Capital Units, Net Amount
Plaintiff sought value, up to
Loss Contingency Plaintiff Sought Value
Loss contingency plaintiff sought value.
Payments made
Loss Contingency Accrual, Payments
Preferred share dividends
Dividends, Preferred Stock, Cash
Fair value of asset (liability) - beginning
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs
Unrealized gain (loss) on Foreign-Exchange Contract included in financing charges
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings
Fair value of asset - ending
Debt Conversion Description [Axis]
Debt Conversion Description [Axis]
Debt Conversion, Name [Domain]
Debt Conversion, Name [Domain]
Initial Instalment [Member]
Initial Instalment [Member]
Initial Instalment [Member]
Final Instalment [Member]
Final Instalment [Member]
Final Instalment [Member]
Long-term debt, face amount
Long-term debt, interest rate
Debt Instrument, Interest Rate, Stated Percentage
Proceeds from convertible debt
Debt issuance costs
Debt Issuance Costs, Gross
Derecognition of deferred financing costs
Payments of Financing Costs
Interest on short-term notes
Schedule of Finite-Lived Intangible Assets [Table]
Schedule of Finite-Lived Intangible Assets [Table]
Finite-Lived Intangible Assets by Major Class [Axis]
Finite-Lived Intangible Assets by Major Class [Axis]
Finite-Lived Intangible Assets, Major Class Name [Domain]
Finite-Lived Intangible Assets, Major Class Name [Domain]
Computer Applications Software [Member]
Computer Software, Intangible Asset [Member]
Other [Member]
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets
Finite-Lived Intangible Assets, Gross
Accumulated Amortization
Finite-Lived Intangible Assets, Accumulated Amortization
Development in Progress
Finite Lived Intangible Assets Development In Progress
Finite Lived Intangible Assets Development In Progress
Total
Finite-Lived Intangible Assets, Net
Segment Reporting [Abstract]
Segmented Reporting
Segment Reporting Disclosure [Text Block]
Debt and Credit Agreements
Debt Disclosure [Text Block]
Regulatory Matters [Table]
Regulatory Matters [Table]
Regulatory Matters [Table]
Restatement [Axis]
Restatement [Axis]
Restatement [Domain]
Restatement [Domain]
Change in Distribution Rate Adjustment [Member]
Restatement Adjustment [Member]
Regulatory Liability [Axis]
Regulatory Liability [Axis]
Regulatory Liability [Domain]
Regulatory Liability [Domain]
Deferred Income Tax Regulatory Asset [Member]
Deferred Income Tax Charge [Member]
Regulatory Asset [Axis]
Regulatory Asset [Axis]
Regulatory Asset [Domain]
Regulatory Asset [Domain]
Foregone Revenue Deferral [Member]
Foregone Revenue Deferral [Member]
Foregone Revenue Deferral [Member]
Pension Benefit Regulatory Asset [Member]
Pension Costs [Member]
Post-Retirement and Post-Employment Benefits [Member]
Polychlorinated Biphenyl Liability [Member]
Polychlorinated Biphenyl Liability [Member]
Polychlorinated Biphenyl Liability [Member]
Environmental [Member]
Environmental [Member]
Environmental [Member]
Stock-Based Compensation [Member]
Share Based Compensation [Member]
Share Based Compensation [Member]
Pension Cost Differential [Member]
Pension Cost Variance [Member]
Pension Cost Variance [Member]
Regulatory Matters [Line Items]
Regulatory Matters [Line Items]
Regulatory Matters [Line Items]
Increase (decrease) in income tax expense including the impact of a change in enacted tax rates
Income Tax Reconciliation Change In Enacted Tax Rates
Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) attributable to regulatory accounting.
Impairment of regulatory assets
Amount of Impairment to Carrying Amount of Regulatory Assets
Increase (decrease) in regulatory liabilities
Increase (Decrease) in Regulatory Liabilities
Increase (decrease) to regulatory assets
Increase Decrease To Regulatory Assets
Increase (decrease) to regulatory assets.
Deferred income tax expense (recovery)
Deferred Income Tax Expense (Benefit)
Increase (decrease) in other comprehensive income
Increase Decrease In Other Comprehensive Income One
Increase (decrease) in other comprehensive income one attributable to regulated accounting.
Increase (decrease) in operation, maintenance and administration expenses
Increase Decrease To Selling, General And Administrative Expenses
Increase (decrease) to selling, general and administrative expenses attributable to regulatory accounting.
Increase (decrease) in financing chargers
Increase Decrease In Financing Charges
Increase (decrease) in financing charges attributable to regulatory accounting.
Increase (decrease) to operation, maintenance, administration and depreciation expenses
Increase Decrease To Operation Maintenance Administration And Depreciation Expense
Increase (decrease) to operation maintenance administration and depreciation expense.
Increase (decrease) in revenue
Increase Decrease In Revenue
Increase (decrease) in revenue attributable to regulatory accounting.
Increase (decrease) in capital expenditures
Increase (Decrease) In Capital Expenditures
Increase (Decrease) In Capital Expenditures
Expenditures
Current income tax expense
Current Income Tax Expense (Benefit)
Total income tax expense (recovery)
Income Tax Expense (Benefit)
Stock-Based Compensation
Share-based Payment Arrangement [Text Block]
Floating-rate Series 31 notes due 2019 [Member]
Floating Rate Series Thirty One Notes Due Two Thousand Nineteen [Member]
Floating Rate Series Thirty One Notes Due Two Thousand Nineteen [Member]
4.40% Series 20 Notes Due 2020 [Member]
Four Point Four Zero Percent Series Twenty Notes Due Two Thousand Twenty [Member]
Four Point Four Zero Percent Series Twenty Notes Due Two Thousand Twenty [Member]
1.84% Series 34 Notes Due 2021 [Member]
One Point Eight Four Percent Series Thirty Four Notes Due Two Thousand Twenty One [Member]
One point eight four percent series thirty four notes due two thousand twenty one.
2.57% Series 39 Notes Due 2021 [Member]
Two Point Five Seven Percent Series Thirty Nine Notes Due Two Thousand Twenty One [Member]
Two Point Five Seven Percent Series Thirty Nine Notes Due Two Thousand Twenty One [Member]
3.20% Series 25 Notes Due 2022 [Member]
Three Point Two Zero Percent Series Twenty Five Notes Due Two Thousand Twenty Two [Member]
Three Point Two Zero Percent Series Twenty Five Notes Due Two Thousand Twenty Two [Member]
2.54% Series 42 Notes Due 2024 [Member]
Two Point Five Four Percent Series Forty Two Notes Due Two Thousand Twenty Four [Member]
Two Point Five Four Percent Series Forty Two Notes Due Two Thousand Twenty Four [Member]
2.97% Series 40 Notes Due 2025 [Member]
Two Point Nine Seven Percent Series Forty Notes Due Two Thousand Twenty Five [Member]
Two Point Nine Seven Percent Series Forty Notes Due Two Thousand Twenty Five [Member]
2.77% Series 35 Notes Due 2026 [Member]
Two Point Seven Seven Percent Series Thirty Five Notes Due Two Thousand Twenty Six [Member]
Two point seven seven percent series thirty five notes due two thousand twenty six.
3.02% Series 43 Notes Due 2029 [Member]
Three Point Zero Two Percent Series Forty Three Notes Due Two Thousand Twenty Nine [Member]
Three Point Zero Two Percent Series Forty Three Notes Due Two Thousand Twenty Nine [Member]
7.35% Debentures Due 2030 [Member]
Seven Point Thirty Five Percent Debentures Due Two Thousand Thirty [Member]
Seven Point Thirty Five Percent Debentures Due Two Thousand Thirty [Member]
6.93% Series 2 Notes Due 2032 [Member]
Six Point Nine Three Percent Series Two Notes Due Two Thousand Thirty Two [Member]
Six Point Nine Three Percent Series Two Notes Due Two Thousand Thirty Two [Member]
6.35% Series 4 Notes Due 2034 [Member]
Six Point Three Five Percent Series Four Notes Due Two Thousand Thirty Four [Member]
Six Point Three Five Percent Series Four Notes Due Two Thousand Thirty Four [Member]
5.36% Series 9 Notes Due 2036 [Member]
Five Point Thirty Six Percent Series Nine Notes Due Two Thousand Thirty Six [Member]
Five Point Thirty Six Percent Series Nine Notes Due Two Thousand Thirty Six [Member]
4.89% Series 12 Notes Due 2037 [Member]
Four Point Eighty Nine Percent Series Twelve Notes Due Two Thousand Thirty Seven [Member]
Four Point Eighty Nine Percent Series Twelve Notes Due Two Thousand Thirty Seven [Member]
6.03% Series 17 Notes Due 2039 [Member]
Six Point Zero Three Percent Series Seventeen Notes Due Two Thousand Thirty Nine [Member]
Six Point Zero Three Percent Series Seventeen Notes Due Two Thousand Thirty Nine [Member]
5.49% Series 18 Notes Due 2040 [Member]
Five Point Forty Nine Percent Series Eighteen Notes Due Two Thousand Forty [Member]
Five Point Forty Nine Percent Series Eighteen Notes Due Two Thousand Forty [Member]
4.39% Series 23 Notes Due 2041 [Member]
Four Point Thirty Nine Percent Series Twenty Three Notes Due Two Thousand Forty One [Member]
Four Point Thirty Nine Percent Series Twenty Three Notes Due Two Thousand Forty One [Member]
6.59% Series 5 Notes Due 2043 [Member]
Six Point Fifty Nine Percent Series Five Notes Due Two Thousand Forty Three [Member]
Six Point Fifty Nine Percent Series Five Notes Due Two Thousand Forty Three [Member]
4.59% Series 29 Notes Due 2043 [Member]
Four Point Five Nine Percent Series Twenty Nine Notes Due Two Thousand Forty Three [Member]
Four Point Five Nine Percent Series Twenty Nine Notes Due Two Thousand Forty Three [Member]
4.17% Series 32 Notes Due 2044 [Member]
Four Point Seventeen Percent Series Thirty Two Notes Due Two Thousand Forty Four [Member]
Four Point Seventeen Percent Series Thirty Two Notes Due Two Thousand Forty Four [Member]
5.00% Series 11 Notes Due 2046 [Member]
Five Point Zero Zero Percent Series Eleven Notes Due Two Thousand Forty Six [Member]
Five Point Zero Zero Percent Series Eleven Notes Due Two Thousand Forty Six [Member]
3.91% Series 36 Notes Due 2046 [Member]
Three Point Nine One Percent Series Thirty Six Notes Due Two Thousand Forty Six [Member]
Three point nine one percent series thirty six notes due two thousand forty six.
3.72% Series 38 Notes Due 2047 [Member]
Three Point Seven Two Percent Series Thirty Eight Notes Due Two Thousand Forty Seven [Member]
Three point seven two percent series thirty eight notes due two thousand forty seven.
3.63% Series 41 Notes Due 2049 [Member]
Three Point Six Three Percent Series Forty One Notes Due Two Thousand Forty Nine [Member]
Three Point Six Three Percent Series Forty One Notes Due Two Thousand Forty Nine [Member]
3.64% Series 44 Notes Due 2050 [Member]
Three Point Six Four Percent Series Forty Four Notes Due Two Thousand Twenty Fifty [Member]
Three Point Six Four Percent Series Forty Four Notes Due Two Thousand Twenty Fifty [Member]
4.00% Series 24 Notes Due 2051 [Member]
Four Point Zero Zero Percent Series Twenty Four Notes Due Two Thousand Fifty One [Member]
Four Point Zero Zero Percent Series Twenty Four Notes Due Two Thousand Fifty One [Member]
3.79% Series 26 Notes Due 2062 [Member]
Three Point Seventy Nine Percent Series Twenty Six Notes Due Two Thousand Sixty Two [Member]
Three Point Seventy Nine Percent Series Twenty Six Notes Due Two Thousand Sixty Two [Member]
4.29% Series 30 Notes Due 2064 [Member]
Four Point Twenty Nine Percent Series Thirty Notes Due Two Thousand Sixty Four [Member]
Four Point Twenty Nine Percent Series Thirty Notes Due Two Thousand Sixty Four [Member]
6.6% Senior Secured Bonds due 2023 [Member]
Six Point Six Percent Senior Secured Bonds Due Two Thousand And Twenty Three [Member]
Six point six percent senior secured bonds due two thousand and twenty three.
4.6% Note Payable due 2023 [Member]
Four Point Six Percent Notes Payable Due Two Thousand And Twenty Three [Member]
Four point six percent notes payable due two thousand and twenty three.
Medium Term Note Program [Member]
Medium Term Note Program [Member]
Medium Term Note Program [Member]
Medium-term Notes [Member]
Medium-term Notes [Member]
Long-term debt, market value
Long Term Debt Market Value
Fair value of debt instrument at date of acquisition less principal payments.
Long-term debt, Total
Long Term Debt Carrying Amount
Carrying amount of debt instrument, before unamortized (discount) premium, debt issuance costs, and unrealized mark-to-market gains and losses, of long-term debt.
Add: Net unamortized debt premiums
Debt Instrument, Unamortized Premium, Current
Add: Unrealized mark-to-market loss (gain)
Unrealized Mark To Market Loss Gain
Unrealized mark to market loss gain.
Less: Unamortized deferred debt issuance costs
Debt Issuance Costs, Current, Net
Total long-term debt
Long-term Debt
Hedged portion of debt
Hedged Portion of Long-Term Debt
Hedged portion of long-term debt.
Debt instrument maximum borrowing capacity
Debt Instrument, Maximum Borrowing Capacity
Debt Instrument, Maximum Borrowing Capacity
Debt instrument unused borrowing capacity
Debt Instrument, Unused Borrowing Capacity, Amount
Long-term debt issued
Proceeds from Issuance of Long-term Debt
Loan repaid and redeemed
Repayments of Debt
Class of Stock [Axis]
Class of Stock [Axis]
Class of Stock [Domain]
Class of Stock [Domain]
Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Member]
Number of shares issued (in shares)
Common Stock, Shares, Issued
Number of shares outstanding (in shares)
Preferred shares issued (in shares)
Preferred Stock, Shares Issued
Preferred shares outstanding (in shares)
Preferred Stock, Shares Outstanding
Weighted average number of shares outstanding (in shares)
Cumulative preferred dividend rate (in cad per dollar)
Preferred Stock, Dividend Rate, Per-Dollar-Amount
Cumulative preferred dividend rate
Preferred Stock, Dividend Rate, Percentage
Redemption price (in cad per share)
Preferred Stock, Redemption Price Per Share
Number of preferred dividends in arrears
Preferred Stock, Amount of Preferred Dividends in Arrears
Number of shares issued upon conversion (in shares)
Convertible Preferred Stock, Shares Issued upon Conversion
Schedule of Earnings Per Share, Basic and Diluted
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Actuarial loss (gain)
Defined Benefit Plan Regulatory Assets Not Recognized As Components Of Net Periodic Benefit Costs Actuarial Loss
Components of regulatory assets that have not been recognized as components of net periodic benefit costs related to actuarial loss.
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months
2021
Lessee, Operating Lease, Liability, Payments, Due Year Two
2022
Lessee, Operating Lease, Liability, Payments, Due Year Three
2023
Lessee, Operating Lease, Liability, Payments, Due Year Four
2024
Lessee, Operating Lease, Liability, Payments, Due Year Five
Thereafter
Lessee, Operating Lease, Liability, Payments, Due after Year Five
Total undiscounted minimum lease payments
Lessee, Operating Lease, Liability, Payments, Due
Less: discounting minimum lease payments to present value
Lessee, Operating Lease, Liability, Undiscounted Excess Amount
Total discounted minimum lease payments
Committed amounts for leases that have not yet commenced
Lessee, Operating Lease, Lease Not Yet Commenced, Undiscounted Amount
Lessee, Operating Lease, Lease Not Yet Commenced, Undiscounted Amount
Lessee, Lease, Description [Table]
Lessee, Lease, Description [Table]
Lessee, Lease, Description [Line Items]
Lessee, Lease, Description [Line Items]
Operating lease term
Lessee, Operating Lease, Term of Contract
Operating lease renewal term
Lessee, Operating Lease, Renewal Term
Outsourcing agreements, year 1
Outsourcing Agreements Future Minimum Payments Due in Next Twelve Months
Amount of required minimum payments under outsourcing agreements due in next twelve months.
Outsourcing agreements, year 2
Outsourcing Agreements Future Minimum Payments Due in Second Year
Amount of required minimum payments under outsourcing agreements due in second year.
Outsourcing agreements, year 3
Outsourcing Agreements Future Minimum Payments Due in Third Year
Amount of required minimum payments under outsourcing agreements due in third year.
Outsourcing agreements, year 4
Outsourcing Agreements Future Minimum Payments Due in Fourth Year
Amount of required minimum payments under outsourcing agreements due in fourth year.
Outsourcing agreements, year 5
Outsourcing Agreements Future Minimum Payments Due in Fifth Year
Amount of required minimum payments under outsourcing agreements due in fifth year.
Outsourcing agreements, thereafter
Outsourcing Agreements Future Minimum Payments Due After Fifth Year
Amount of required minimum payments under outsourcing agreements due after fifth year.
Long-term software/meter agreement, year 1
Long Term Software and Meter Agreement Future Minimum Payments Due in Next Twelve Months
Amount of required minimum payments under Long term software and meter agreement due in next twelve months.
Long-term software/meter agreement, year 2
Long Term Software and Meter Agreement Future Minimum Payments Due in Second Year
Amount of required minimum payments under Long term software and meter agreement due in second year.
Long-term software/meter agreement, year 3
Long Term Software and Meter Agreement Future Minimum Payments Due in Third Year
Amount of required minimum payments under Long term software and meter agreement due in third year.
Long-term software/meter agreement, year 4
Long Term Software and Meter Agreement Minimum Payments Due in Fourth Year
Amount of required minimum payments under Long term software and meter agreement due in fourth year.
Long-term software/meter agreement, year 5
Long Term Software and Meter Agreement Future Minimum Payments Due in Fifth Year
Amount of required minimum payments under Long term software and meter agreement due in fifth year.
Long-term software/meter agreement, thereafter
Long Term Software and Meter Agreement Future Minimum Payments Due After Fifth Year
Amount of required minimum payments under Long term software and meter agreement due after fifth year.
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]
Regulatory Assets [Member]
Regulatory Assets [Member]
Regulatory assets.
Schedule Of Components Of Regulatory Assets Expected To Be Amortized As Components Of Net Periodic Benefit Cost [Line Items]
Schedule Of Components Of Regulatory Assets Expected To Be Amortized As Components Of Net Periodic Benefit Cost [Line Items]
Schedule Of Components Of Regulatory Assets Expected To Be Amortized As Components Of Net Periodic Benefit Cost [Line Items]
Actuarial loss (gain)
Defined Benefit Plan Future Amortization Of Actuarial Loss On Regulatory Assets
Amount included in regulatory assets related to actuarial loss expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.
2020
Estimated Future Environmental Expenditures Due In One Year
Estimated future environmental expenditures due in one year.
2021
Estimated Future Environmental Expenditures Due In Two Years
Estimated future environmental expenditures due in two year.
2022
Estimated Future Environmental Expenditures Due In Three Years
Estimated future environmental expenditures due in three year.
2023
Estimated Future Environmental Expenditures Due In Four Years
Estimated future environmental expenditures due in four year.
2024
Estimated Future Environmental Expenditures Due In Five Years
Estimated future environmental expenditures due in five year.
Thereafter
Estimated Future Environmental Expenditures Due Thereafter
Estimated future environmental expenditures due thereafter.
Total
Estimated Future Environmental Expenditures Due
Estimated future environmental expenditures due.
New Accounting Pronouncements or Change in Accounting Principle [Table]
New Accounting Pronouncements or Change in Accounting Principle [Table]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Weighted average discount rate
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate
Rate of compensation scale escalation (long-term)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase
Rate of cost of living increase
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Cost Of Living Increase
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Cost Of Living Increase
Rate of increase in health care cost trends
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Health Care Cost Trend Rate
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Health Care Cost Trend Rate
Document And Entity Information [Abstract]
Document And Entity Information [Abstract]
Document Type
Document Type
Amendment Flag
Amendment Flag
Document Period End Date
Document Period End Date
Document Fiscal Year Focus
Document Fiscal Year Focus
Document Fiscal Period Focus
Document Fiscal Period Focus
Entity Registrant Name
Entity Registrant Name
Entity Central Index Key
Entity Central Index Key
Current Fiscal Year End Date
Current Fiscal Year End Date
Entity Current Reporting Status
Entity Current Reporting Status
Entity Common Stock, Shares Outstanding
Entity Common Stock, Shares Outstanding
Entity Emerging Growth Company
Entity Emerging Growth Company
Commitments [Table]
Commitments [Table]
Commitments [Table]
Long-Term Software/Meter Agreement [Member]
Long Term Software And Meter Agreement [Member]
Long term software and meter agreement.
Trilliant Agreement [Member]
Trilliant Agreement [Member]
Trilliant agreement.
Commitments [Line Items]
Commitments [Line Items]
Commitments [Line Items]
Agreement renewal term
Long Term Purchase Commitment Renewal Term
Long term purchase commitment renewal term.
Typical terms of irrevocable operating lease
Operating lease renewal options
Summary of Share Grant Activity
Share-based Payment Arrangement, Option, Activity [Table Text Block]
Summary of Number of DSUs
Schedule of Deferred Compensation Arrangement with Individual, Share-based Payments [Table Text Block]
Summary of Number of PSUs and RSUs
Schedule Of Performance Shares And Restricted Stock Units Activity [Table Text Block]
Schedule Of Performance Shares And Restricted Stock Units Activity
Schedule of Credit Facilities
Schedule of Line of Credit Facilities [Table Text Block]
Schedule of Outstanding Long-Term Debt
Schedule of Long-term Debt Instruments [Table Text Block]
Schedule of Long-Term Debt
Schedule Of Identified Noncurrent Liabilities [Table Text Block]
Schedule of identified noncurrent liabilities.
Summary of Principal Repayments and Related Weighted Average Interest Rates
Schedule of Maturities Principal and Interest of Long-term Debt [Table Text Block]
Tabular disclosure of the combined aggregate amount of maturities and weighted average interest rates for long-term borrowings.
Description of the Business
Business Description and Basis of Presentation [Text Block]
Post Retirement and Employment Benefits Regulatory Assets [Member]
Postretirement And Employment Benefits Regulatory Assets [Member]
Postretirement and employment benefits regulatory assets.
Actuarial loss (gain) for the year
Amortization of actuarial losses
Defined Benefit Plan Actuarial Loss Amortization
Defined benefit plan actuarial loss amortization.
Amounts not subject to regulatory treatment
Defined Benefit Plan, Amounts Not Subject To Regulatory Treatment
Defined Benefit Plan, Amounts Not Subject To Regulatory Treatment
Total actuarial gains and losses and prior service costs
Recognition Of Actuarial Gains And Losses And Amortization Of Prior Service Cost
Recognition of actuarial gains and losses and amortization of prior service cost.
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations
Asset Retirement Obligation Disclosure [Text Block]
Level 1 [Member]
Fair Value, Inputs, Level 1 [Member]
Level 2 [Member]
Fair Value, Inputs, Level 2 [Member]
Pooled Funds [Member]
Pooled Funds [Member]
Pooled Funds [Member]
Cash and Cash Equivalents [Member]
Defined Benefit Plan, Cash and Cash Equivalents [Member]
Short-term Securities [Member]
Money Market Funds [Member]
Derivative instruments [Member]
Defined Benefit Plan, Derivative [Member]
Corporate Shares - Canadian [Member]
Debt Security, Corporate, US [Member]
Corporate Shares - Foreign [Member]
Debt Security, Corporate, Non-US [Member]
Bonds and Debentures - Canadian [Member]
Bonds And Debentures [Member]
Bonds And Debentures [Member]
Bonds and debentures - Foreign [Member]
Foreign Bonds And Debentures [Member]
Foreign Bonds And Debentures [Member]
Defined Benefit Plan, Plan Liabilities, Category [Axis]
Defined Benefit Plan, Plan Liabilities, Category [Axis]
Defined Benefit Plan, Plan Liabilities, Category [Axis]
Defined Benefit Plan, Plan Liabilities, Category [Domain]
Defined Benefit Plan, Plan Liabilities, Category [Domain]
[Domain] for Defined Benefit Plan, Plan Liabilities, Category [Axis]
Total fair value of plan assets
Pension Plan Assets Measured At Fair Value
Pension plan assets measured at fair value.
Total fair value of plan liabilities
Pension Plan Liabilities Measured At Fair Value
Pension Plan Liabilities Measured At Fair Value
Interest and dividend receivable excluded from fair value of pension plan assets
Interest And Dividend Receivable Excluded From Pension Plan Assets Fair Value
Interest and dividend receivable excluded from pension plan assets fair value.
Accruals for pension administration expense excluded from fair value of pension plan assets
Accruals For Pension Administration Expense And Foreign Exchange Contracts Payable Excluded From Pension Plan Assets Fair Value
Accruals for pension administration expense and foreign exchange contracts payable excluded from pension plan assets fair value.
Sale of investments receivable excluded from fair value of pension plan assets
Sale Of Investments Receivable Excluded From Pension Plan Assets Fair Value
Sale of investments receivable excluded from pension plan assets fair value.
Purchase of investments payable excluded from fair value of pension plan assets
Purchase Of Investments Payable Excluded From Pension Plan Assets Fair Value
Purchase of investments payable excluded from pension plan assets fair value.
Financing Charges
Interest Income and Interest Expense Disclosure [Text Block]
Number of reportable segments
Number of Reportable Segments
Number of local distribution companies (more than)
Number Of Local Distribution Companies
Number of local distribution companies.
Noncontrolling Interest
Noncontrolling Interest Disclosure [Text Block]
Year 1 [Member]
Debt Instrument Maturity Period Year One [Member]
Debt Instrument Maturity Period Year One [Member]
Year 2 [Member]
Debt Instrument Maturity Period Year Two [Member]
Debt Instrument Maturity Period Year Two [Member]
Year 3 [Member]
Debt Instrument Maturity Period Year Three [Member]
Debt Instrument Maturity Period Year Three [Member]
Year 4 [Member]
Debt Instrument Maturity Period Year Four [Member]
Debt Instrument Maturity Period Year Four [Member]
Year 5 [Member]
Debt Instrument Maturity Period Year Five [Member]
Debt Instrument Maturity Period Year Five [Member]
5 Years, Total [Member]
Debt Instrument Maturity Period At End of Fifth Year [Member]
Debt Instrument Maturity Period At End of Fifth Year [Member]
Years 6-10 [Member ]
Debt Instrument Maturity Period Between Six To Ten Years [Member ]
Debt Instrument Maturity Period Between Six To Ten Years [Member ]
Thereafter [Member]
Debt Instrument Maturity Period Over Ten Years [Member]
Debt Instrument Maturity Period Over Ten Years [Member]
Long-term debt principal repayments, 1 year
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months
Long-term debt principal repayments, 2 years
Long-term Debt, Maturities, Repayments of Principal in Year Two
Long-term debt principal repayments, 3 years
Long-term Debt, Maturities, Repayments of Principal in Year Three
Long-term debt principal repayments, 4 years
Long-term Debt, Maturities, Repayments of Principal in Year Four
Long-term debt principal repayments, 5 years
Long-term Debt, Maturities, Repayments of Principal in Year Five
Long-term Debt Principal repayments during 5 years
Long Term Debt Maturities Aggregate Repayments Of Principal Next Five Years
Long Term Debt Maturities Aggregate Repayments Of Principal Next Five Years
Long-term debt principal repayments, 6 – 10 years
Long Term Debt, Maturities, Repayments of Principal Between Six to Ten Year
Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing between sixth to tenth fiscal year following the latest fiscal year.
Long-term debt principal repayments, thereafter
Long Term Debt, Maturities, Repayments of Principal in Over Ten Years
Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in over the tenth fiscal year following the latest fiscal year.
Long-term debt, Total
Interest payments
Interest Expense, Debt
Weighted average interest rate
Debt, Weighted Average Interest Rate
Other Commitments [Table]
Other Commitments [Table]
Credit Facilities [Member]
Credit Facilities [Member]
Credit Facilities [Member]
Letters Of Credit [Member]
Letter of Credit [Member]
Retirement Compensation Arrangements [Member]
Letters Of Credit, Retirement Compensation Arrangements [Member]
Letters Of Credit, Retirement Compensation Arrangements
Prudential Support From IESO [Member]
Letters Of Credit, Prudential Support [Member]
Letters Of Credit, Prudential Support
Debt Service Reserve Requirements [Member]
Letters Of Credit, Debt Service Reserve Requirements [Member]
Letters Of Credit, Debt Service Reserve Requirements
Various Operating Purposes [Member]
Letters Of Credit, Various Operating Purposes [Member]
Letters Of Credit, Various Operating Purposes
Other Commitments [Line Items]
Other Commitments [Line Items]
Other commitment, year 2
Other Commitment, Due in Second Year
Other commitment, year 3
Other Commitment, Due in Third Year
Other commitment, year 4
Other Commitment, Due in Fourth Year
Other commitment, year 5
Other Commitment, Due in Fifth Year
Other commitment, thereafter
Other Commitment, Due after Fifth Year
Schedule of Movements in Noncontrolling Interest
Summary Of Noncontrolling Interest [Table Text Block]
Summary Of Noncontrolling Interest
Long-term debt payable within one year
Long-term Debt, Current Maturities
Short-term notes payable
Commercial Paper
Less: cash and cash equivalents
Cash and Cash Equivalents, at Carrying Value
Net Long-term debt payable within one year
Long Term Debt Current Net of Cash and Cash Equivalents
Long Term Debt Current Net of Cash and Cash Equivalents
Long-term debt
Long-term Debt, Excluding Current Maturities
Convertible debentures (Notes 17, 18)
Preferred shares
Preferred Stock, Value, Outstanding
Common shares
Common Stock, Value, Outstanding
Retained earnings
Retained Earnings (Accumulated Deficit)
Total capital
Capitalization, Long-term Debt and Equity
Pension and Post-Retirement and Post-Employment Benefits
Compensation and Employee Benefit Plans [Text Block]
Schedule of Movements in Environmental Liabilities
Rollforward Of Environmental Liability [Table Text Block]
Rollforward Of Environmental Liability Table [Text Block]
Reconciliation between Undiscounted Basis of Environmental Liabilities and Amount Recognized on Consolidated Balance Sheets
Reconciliation Between Undiscounted Basis And Amount Recognized In Consolidated Balance Sheets Factoring Discount Rate [Table Text Block]
Reconciliation Between Undiscounted Basis And Amount Recognized In Consolidated Balance Sheets Factoring Discount Rate [Table Text Block]
Schedule of Estimated Future Environmental Expenditures
Estimated Future Environmental Expenditures [Table Text Block]
Estimated Future Environmental Expenditures [Table Text Block]
Intangible Assets
Intangible Assets Disclosure [Text Block]
Accounts Receivable
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]
Assets
Assets [Abstract]
Current assets:
Assets, Current [Abstract]
Cash and cash equivalents
Accounts receivable (Note 8)
Accounts Receivable, after Allowance for Credit Loss, Current
Due from related parties (Note 29)
Due from Related Parties, Current
Other current assets (Note 9)
Other Assets, Current
Total current assets
Assets, Current
Property, plant and equipment (Note 10)
Other long-term assets:
Assets, Noncurrent [Abstract]
Regulatory assets (Note 12)
Regulatory Assets, Noncurrent
Deferred income tax assets
Deferred Income Tax Assets, Net
Intangible assets (Note 11)
Intangible Assets, Net (Excluding Goodwill)
Goodwill
Goodwill
Other assets
Total other long-term assets
Assets, Noncurrent
Total assets
Assets
Liabilities
Liabilities [Abstract]
Current liabilities:
Liabilities, Current [Abstract]
Short-term notes payable (Note 16)
Long-term debt payable within one year (Notes 16, 18)
Accounts payable and other current liabilities (Note 14)
Due to related parties (Note 29)
Due to Related Parties, Current
Total current liabilities
Liabilities, Current
Long-term liabilities:
Liabilities, Noncurrent [Abstract]
Long-term debt (includes $351 measured at fair value; 2018 - $845) (Notes 16, 18)
Regulatory liabilities (Note 12)
Regulatory Liability, Noncurrent
Deferred income tax liabilities
Deferred Income Tax Liabilities, Net
Other long-term liabilities (Note 15)
Total Long-term liabilities
Liabilities, Noncurrent
Total liabilities
Liabilities
Contingencies and Commitments (Notes 31, 32)
Commitments and Contingencies
Subsequent Events (Note 34)
Subsequent Events
Subsequent Events
Noncontrolling interest subject to redemption (Note 28)
Equity
Common shares (Note 24)
Preferred shares (Note 24)
Additional paid-in capital (Note 27)
Additional Paid in Capital
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss), Net of Tax
Hydro One shareholders’ equity
Stockholders' Equity Attributable to Parent
Noncontrolling interest (Note 28)
Total equity
Total liabilities, preferred shares, noncontrolling interest subject to redemption and equity
Liabilities and Equity
$50 Million of MTN Series 33 Notes [Member]
Fifty Million Of Medium Term Note Series Thirty Three Notes One [Member]
Fifty Million of Medium Term Note Series Thirty Three Notes One [Member]
$500 million of MTN Series 37 notes [Member]
Five Hundred Million Of Medium Term Note Series Thirty Seven Notes [Member]
Five hundred million of medium term note series thirty seven notes.
Other Notes and Debentures [Member]
Other Notes And Debentures [Member]
Other Notes And Debentures [Member]
Carrying value
Fair value
Long-term Debt, Fair Value
Accounts receivable
Increase (Decrease) in Accounts Receivable
Due from related parties
Increase (Decrease) in Due from Related Parties, Current
Other assets
Increase (Decrease) in Other Operating Assets
Accounts payable
Increase (Decrease) in Accounts Payable
Accrued liabilities
Increase (Decrease) in Accrued Liabilities
Due to related parties
Increase (Decrease) in Due to Related Parties, Current
Accrued interest
Increase (Decrease) In Accrued Interest Payable
Increase (Decrease) In Accrued Interest Payable
Long-term accounts payable and other liabilities
Increase Decrease In Non Current Accounts Payable And Other Operating Liabilities
Increase decrease in non-current accounts payable and other operating liabilities.
Post-retirement and post-employment benefit liability
Increase (decrease) in post-retirement and post-employment benefit liability
Increase (decrease) in post-retirement and post-employment benefit liability
Changes in non-cash balances related to operations, Total
Increase (Decrease) in Operating Capital
Capital investment, property, plant and equipment
Capital Investments In Property Plant And Equipment
Capital Investments In Property Plant And Equipment
Capital investments, intangible assets
Capital Investments In Intangible Assets
Capital Investments In Intangible Assets
Capital investments
Capital Investments
Capital Investments
Reconciling items, property plant and equipment
Capitalized Depreciation And Net Change In Accruals Included In Capital Investments In Property Plant And Equipment
Capitalized Depreciation And Net Change In Accruals Included In Capital Investments In Property Plant And Equipment
Reconciling items, intangible assets
Net Change In Accruals Included In Capital Investments In Intangible Assets
Net Change In Accruals Included In Capital Investments In Intangible Assets
Reconciling items, property plant and equipment, total
Net Change In Accruals Included In Capital Investments
Net Change In Accruals Included In Capital Investments
Cash outflow for capital expenditures, property plant and equipment
Payments to Acquire Property, Plant, and Equipment
Cash outflow for capital expenditures, intangible assets
Payments to Acquire Intangible Assets
Cash outflow for capital expenditures, total
Payments to Acquire Productive Assets
Capital contributions received
Capital Contributions Received
Capital contributions received.
Net interest paid
Interest Paid, Excluding Capitalized Interest, Operating Activities
Income taxes paid
Income Taxes Paid
Fair Value Inputs Assets Liabilities Quantitative Information [Table]
Fair Value Inputs Assets Liabilities Quantitative Information [Table]
Fair value inputs assets liabilities quantitative information.
Hedging Relationship [Axis]
Hedging Relationship [Axis]
Hedging Relationship [Domain]
Hedging Relationship [Domain]
Fair Value Hedging [Member]
Fair Value Hedging [Member]
Cash Flow Hedging [Member]
Cash Flow Hedging [Member]
Measurement Basis [Axis]
Measurement Basis [Axis]
Fair Value Measurement [Domain]
Fair Value Measurement [Domain]
Portion at Fair Value Measurement [Member]
Portion at Fair Value Measurement [Member]
Carrying Value [Member]
Reported Value Measurement [Member]
Fair Value [Member]
Estimate of Fair Value Measurement [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Assets:
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative instrument - Foreign-Exchange Contract (Notes 4, 18)
Derivative Asset, Current
Total assets
Assets, Fair Value Disclosure
Liabilities:
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion, fair value
Fair value hedge - interest-rate swap
Derivative Liability, Noncurrent
Total liabilities, fair value
Financial Liabilities Fair Value Disclosure
Income Taxes
Income Tax Disclosure [Text Block]
Summary of Fair Values and Carrying Values of Long-Term Debt
Schedule Of Fair Values And Carrying Values Of Long Term Debt[Table Text Block]
Tabular disclosure of information pertaining to fair value and carrying amount of long-term debt instruments or arrangements.
Summary of Fair Value Hierarchy of Financial Assets and Liabilities
Fair Value, by Balance Sheet Grouping [Table Text Block]
Schedule of Changes in Fair Value of Financial Instruments
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Regulatory assets (Note 12)
Regulatory Assets, Current
Prepaid expenses and other assets
Prepaid Expense and Other Assets, Current
Materials and supplies
Inventory, Raw Materials and Supplies, Gross
Other current assets
Convertible Debentures
Long-term Debt [Text Block]
Summary of Related Party Transactions
Related Party Transactions Details [Table Text Block]
Related party transactions details table.
Long-term inflation rate assumption of current costs
Inflation Rate
Inflation rate.
Future environmental expenditure discount rate
Accrual for Environmental Loss Contingencies, Discount Rate
Increase (decrease) of environmental liability due to revaluation adjustment
2020
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months
2021
2022
2023
2024
Thereafter
Total estimated future benefit payments through to 2029
Defined Benefit Plan Expected Future Benefit Payments
Defined benefit plan expected future benefit payments.
Statement of Cash Flows [Abstract]
Operating activities
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income (loss)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Environmental expenditures
Adjustments for non-cash items:
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization (Note 5)
Regulatory assets and liabilities
Increase (Decrease) in Regulatory Assets and Liabilities
Deferred income tax expense (recovery)
Other
Other Operating Activities, Cash Flow Statement
Changes in non-cash balances related to operations (Note 30)
Net cash from operating activities
Net Cash Provided by (Used in) Operating Activities
Financing activities
Net Cash Provided by (Used in) Financing Activities [Abstract]
Long-term debt repaid
Repayments of Long-term Debt
Short-term notes issued
Proceeds from Issuance of Commercial Paper
Short-term notes repaid
Repayments of Commercial Paper
Convertible debentures redeemed
Dividends paid
Payments of Dividends
Distributions paid to noncontrolling interest
Payments to Noncontrolling Interests
Contributions received from sale of noncontrolling interest (Note 4)
Proceeds from Noncontrolling Interests
Common shares issued
Costs to obtain financing
Proceeds from (Payments for) Other Financing Activities
Net cash from (used in) financing activities
Net Cash Provided by (Used in) Financing Activities
Investing activities
Net Cash Provided by (Used in) Investing Activities [Abstract]
Property, plant and equipment
Intangible assets
Capital contributions received (Note 27)
Other
Payments for (Proceeds from) Other Investing Activities
Net cash used in investing activities
Net Cash Provided by (Used in) Investing Activities
Net change in cash and cash equivalents
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect
Cash and cash equivalents, beginning of year
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents
Cash and cash equivalents, end of year
Financing charges capitalized on property, plant and equipment
Allowance for Funds Used During Construction, Capitalized Interest
Consolidated Statements of Cash Flows
Cash Flow, Supplemental Disclosures [Text Block]
Pension Costs [Member]
Other assets
Other Assets
Pension benefit liability
Post-retirement and post-employment benefit liability
Other Postretirement and Postemployment Benefit Plans Liabilities Noncurrent
Other postretirement and postemployment benefit plans liabilities noncurrent.
Net unfunded status
Defined Benefit Plan, Net Funded Status Of Plan
Defined Benefit Plan, Net Funded Status Of Plan
Post-employment benefit plans
Postemployment Benefits Liability, Noncurrent
Schedule of Segment Reporting Information, by Segment [Table]
Schedule of Segment Reporting Information, by Segment [Table]
Segments [Axis]
Segments [Axis]
Segments [Domain]
Segments [Domain]
Transmission [Member]
Transmission Business [Member]
Transmission business.
Distribution [Member]
Distribution Business [Member]
Distribution business.
Other [Member]
Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information [Line Items]
Depreciation and amortization
Utilities Operating Expense, Depreciation and Amortization
Income before financing charges and income tax expense
Operating Income (Loss)
Capital investments
Total assets
Goodwill
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for doubtful accounts – beginning
Write-offs
Accounts Receivable, Allowance for Credit Loss, Writeoff
Additions to allowance for doubtful accounts
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)
Allowance for doubtful accounts – ending
Total long-term debt
Long-term:
Non Current Deferred Income Taxes [Abstract]
Non current deferred income taxes.
Deferred income tax liabilities
Net deferred income tax assets
Deferred Tax Assets, Net
Depreciation, Amortization And Asset Removal Costs
Depreciation And Amortization [Text Block]
Depreciation And Amortization [Text Block]
Summary of Company's Capital Structure
Schedule of Capitalization [Table Text Block]
Schedule of Accounting Standards Updates Issued by Financial Accounting Standards Board
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]
Leases
Lessee, Operating Leases [Text Block]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations [Line Items]
Long-term inflation assumption of current costs
Discounted future expenditures
Asset Retirement Obligations Discounted Rate
Asset retirement obligations discounted rate.
Revaluation adjustment
Asset Retirement Obligation, Revision of Estimate
Asset retirement obligations recorded
Contingencies
Contingencies Disclosure [Text Block]
Schedule of Other Information Related to Operating Leases
Lease, Cost [Table Text Block]
Schedule of Future Minimum Operating Lease Payments After Adoption
Lessee, Operating Lease, Liability, Maturity [Table Text Block]
Schedule of Future Minimum Operating Lease Payments Before Adoption
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]
Schedule of Supplementary Balance Sheet Information
Assets And Liabilities, Lessee [Table Text Block]
Assets And Liabilities, Lessee [Table Text Block]
Deferred income tax assets
Deferred Tax Assets, Gross [Abstract]
Post-retirement and post-employment benefits expense in excess of cash payments
Deferred Tax Assets Post Retirement And Post Employment Benefit Expense In Excess Of Cash Payments
Deferred Tax Assets Post Retirement And Post Employment Benefit Expense In Excess Of Cash Payments
Non-capital losses
Deferred Tax Assets Non Capital Losses
Deferred tax assets non capital losses.
Non-depreciable capital property
Deferred Tax Assets Non Depreciable Capital Property
Deferred tax assets non depreciable capital property.
Pension obligations
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions
Investment in subsidiaries
Deferred Tax Assets, Investment in Subsidiaries
Tax credit carryforwards
Deferred Tax Assets, Tax Credit Carryforwards
Depreciation and amortization in excess of capital cost allowance
Deferred Tax Assets Depreciation And Amortization
Deferred tax assets depreciation and amortization in excess of capital cost allowance.
Environmental expenditures
Deferred Tax Assets Environmental Reserve
Deferred Tax Assets Environmental Reserve
Other
Deferred Tax Assets, Other
Deferred income tax assets gross
Deferred Tax Assets, Gross
Less: valuation allowance
Total deferred income tax assets
Deferred Tax Assets, Net of Valuation Allowance
Deferred income tax liabilities
Deferred Tax Liabilities, Gross [Abstract]
Capital cost allowance in excess of depreciation and amortization
Deferred Tax Liabilities Capital Cost Allowance In Excess Of Depreciation And Amortization
Deferred Tax Liabilities Capital Cost Allowance In Excess Of Depreciation And Amortization
Regulatory amounts that are not recognized for tax purposes
Deferred Tax Liabilities Regulatory Amounts Receivable That Are Not Recognized For Tax Purposes
Deferred Tax Liabilities Regulatory Amounts Receivable That Are Not Recognized For Tax Purposes
Goodwill
Deferred Tax Liabilities, Goodwill
Other
Deferred Tax Liabilities, Other
Total deferred income tax liabilities
Deferred Tax Liabilities, Net
Other Revenue [Member]
Other Revenue [Member]
Other Revenue [Member]
Revenues
Revenues [Abstract]
Costs
Cost of Revenue [Abstract]
Purchased power (includes $1,818 related party costs; 2018 - $1,648) (Note 29)
Operation, maintenance and administration (Notes 4, 29)
Depreciation, amortization and asset removal costs (Note 5)
Total costs
Costs and Expenses
Financing charges (Note 6)
Income tax expense (recovery) (Note 7)
Net income (loss)
Comprehensive income (loss)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest
Net income (loss) attributable to:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest [Abstract]
Noncontrolling interest (Note 28)
Preferred shareholder
Preferred Stock Dividends and Other Adjustments
Common shareholder
Net income (loss)
Net Income (Loss) Attributable to Parent
Comprehensive income (loss) attributable to:
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Noncontrolling interest (Note 28)
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest
Common shareholder
Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Earnings per common share (Note 26)
Dividends per common share declared (Note 22) (in dollars per share)
Hydro One Limited [Member]
Hydro One Limited [Member]
Hydro One Limited [Member]
Performance Stock Units And Restricted Stock Units [Member]
Performance Stock Units And Restricted Stock Units [Member]
Performance Stock Units And Restricted Stock Units [Member]
Society Share Grant Plan [Member]
Society Share Grant Plan [Member]
Society Share Grant Plan [Member]
Employee Stock Ownership Plan (ESOP) Name [Axis]
Employee Stock Ownership Plan (ESOP) Name [Axis]
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Management Employee Share Ownership Plans [Member]
Management Employee Share Ownership Plans [Member]
Management Employee Share Ownership Plans [Member]
Society Employee Share Ownership Plans [Member]
Society Employee Share Ownership Plans [Member]
Society Employee Share Ownership Plans [Member]
Employee Share Ownership Plan (ESOP) [Member]
Employee Share Ownership Plan [Member]
Employee Share Ownership Plan [Member]
Number of plans
Number Of Plans
Number Of Plans
Requisite service period
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period
Highest percentage of participant's salary towards purchasing common shares
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate
Aggregate number of common shares issuable under the plan (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized
Shares granted (in shares)
Expiration period
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period
Fair value of shares granted
Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Fair Value
Share-based compensation arrangement by share-based payment award options grants in period fair value.
DSU value equivalent to common shares (in shares)
Share-based Compensation Arrangement By Share-based Payment Award, Non-Option Equity Based Instruments, Value Equivalent To Common Shares
Share-based Compensation Arrangement By Share-based Payment Award, Non-Option Equity Based Instruments, Value Equivalent To Common Shares
Compensation expenses
Share-based Payment Arrangement, Expense
Number of shares settled (in shares)
Liability related to share based compensation
Deferred Compensation Liability, Classified, Noncurrent
Closing share price of common shares (in dollars per share)
Share Price
Lowest percentage of participant's salary towards purchasing common shares
Share Based Compensation Arrangement By Share Based Payment Award Minimum Employee Subscription Rate
Share Based Compensation Arrangement By Share Based Payment Award Minimum Employee Subscription Rate
Employer matching contribution, percent of match
Maximum amount contributed by employer
Defined Contribution Plan Maximum Annual Contributions Per Employer Amount
Defined contribution plan maximum annual contributions per employer amount.
Contribution under the plan
Employee Stock Ownership Plan (ESOP), Cash Contributions to ESOP
Grant date total fair value of awards
Share Based Compensation Arrangement By Share Based Payment Award Equity Instrument Other Than Options Grants In Period Fair Value
Share Based Compensation Arrangement By Share Based Payment Award Equity Instrument Other Than Options Grants In Period Fair Value
Vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period
Number of shares modified (in shares)
Share Issued, Number Of Shares Modified
Share Issued, Number Of Shares Modified
Statutory income tax rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
Income tax expense at statutory rate of 26.5% (2018 - 26.5%)
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount
Net temporary differences recoverable in future rates charged to customers:
Net Temporary Differences [Abstract]
Net Temporary Differences [Abstract]
Capital cost allowance in excess of depreciation and amortization
Capital Cost Allowance in Excess of Depreciation and Amortization
Capital Cost Allowance in Excess of Depreciation and Amortization
Non-recurring tax recovery relating to deferred tax asset sharing
Effective Income Tax Rate Reconciliation, Tax Recovery From Deferred Tax Asset Sharing
Effective Income Tax Rate Reconciliation, Tax Recovery From Deferred Tax Asset Sharing
Overheads capitalized for accounting but deducted for tax purposes
Overheads Capitalized for Accounting but Deducted for Tax Purposes
Overheads Capitalized for Accounting but Deducted for Tax Purposes
Interest capitalized for accounting but deducted for tax purposes
Interest Capitalized for Accounting but Deducted for Tax Purposes
Interest Capitalized for Accounting but Deducted for Tax Purposes
Pension and post-retirement benefit contributions in excess of pension expense
Pension Contributions in Excess of Pension Expense
Pension Contributions in Excess of Pension Expense
Environmental expenditures
Environmental Expenditures Reconciliation
Environmental Expenditures Reconciliation
Other
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount
Net temporary differences
Effective Income Tax Rate Reconciliation, Deduction, Amount
Net temporary differences
Net Permanent Differences Reconciliation
Net Permanent Differences Reconciliation
Write-off of unregulated deferred income tax asset (Note 12)
Effective Income Tax Rate Reconciliation, Write Off Of Unregulated Deferred Income Tax Asset
Effective Income Tax Rate Reconciliation, Write Off Of Unregulated Deferred Income Tax Asset
Effective income tax rate
Effective Income Tax Rate Reconciliation, Percent
Schedule of Accounts, Notes, Loans and Financing Receivable [Table]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table]
Billing Status, Type [Axis]
Billing Status, Type [Axis]
Receivables Billing Status [Domain]
Receivables Billing Status [Domain]
Accounts Receivable - Billed [Member]
Billed Revenues [Member]
Accounts Receivable - Unbilled [Member]
Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross
Accounts Receivable, before Allowance for Credit Loss, Current
Allowance for doubtful accounts
Accounts receivable, net
Lease expense
Lease, Cost
Lease payments made
Operating Lease, Payments
Weighted-average remaining lease term1 (years)
Operating Lease, Weighted Average Remaining Lease Term
Weighted-average discount rate
Operating Lease, Weighted Average Discount Rate, Percent
Summary of Segment Information
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Environmental Liabilities
Environmental Liabilities Disclosure [Text Block]
Environmental Liabilities Disclosure [Text Block]
Schedule Of Regulatory Assets And Liabilities [Table]
Schedule Of Regulatory Assets And Liabilities [Table]
Schedule Of Regulatory Assets And Liabilities [Table]
Environmental [Member]
Environmental Restoration Costs [Member]
Post-Retirement and Post-Employment Benefits Non-Service Cost [Member]
Pension And Other Postretirement Plans Non-service Cost [Member]
Pension And Other Postretirement Plans Non-service Cost [Member]
Debt Premium [Member]
Debt Premium [Member]
Debt Premium [Member]
Distribution System Code Exemption [Member]
Distribution System Code Exemption [Member]
Distribution system code exemption.
Other Regulatory Assets [Member]
Other Regulatory Assets [Member]
Other Regulatory Assets [Member]
Tax Rule Changes Variance [Member]
Tax Rule Changes Variance [Member]
Tax Rule Changes Variance [Member]
Distribution Rate Riders [Member]
Distribution Rate Riders [Member]
Distribution Rate Riders [Member]
Green Energy Expenditure Variance [Member]
Green Energy expenditure variance [Member]
Green Energy expenditure variance [Member]
Retail Settlement Variance Account [Member]
Retail Settlement Variance Accounts [Member]
Retail settlement variance accounts.
Earnings Sharing Mechanism Deferral [Member]
Earnings Sharing Mechanism Deferral [Member]
Earnings Sharing Mechanism Deferral [Member]
External Revenue Variance [Member]
External Revenue Variance [Member]
External Revenue Variance [Member]
Deferred Income Tax Regulatory Liability [Member]
Deferred Income Tax Regulatory Liability[Member]
Deferred Income Tax Regulatory Liability[Member]
Other Regulatory Liabilities [Member]
Other Regulatory Liabilities [Member]
Other Regulatory Liabilities [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory assets:
Regulatory Assets [Abstract]
Regulatory Assets [Abstract]
Total regulatory assets
Regulatory Assets
Less: current portion
Regulatory assets
Regulatory liabilities:
Regulatory Liabilities Abstract
Regulatory Liabilities Abstract
Total regulatory liabilities
Regulatory Liabilities
Less: current portion
Regulatory liabilities
Commercial Paper Program [Member]
Commercial Paper [Member]
Maximum borrowing capacity
Commercial Paper Program Maximum Capacity
Maximum authorized borrowing capacity under the commercial paper program without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the commercial paper program.
Maturities days of commercial paper
Debt Instrument, Term
Dividends
Dividend Disclosure [Text Block]
Dividend Disclosure [Text Block]
Commitments
Commitments Disclosure [Text Block]