Equity [Abstract]
Share Capital
Stockholders' Equity Note Disclosure [Text Block]
Business Combinations [Abstract]
Summary of Determination of Fair Value of Assets Acquired and Liabilities Assumed
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]
Compensation and Retirement Disclosure [Abstract]
Pension and Post-Retirement and Post-Employment Benefits
Compensation and Employee Benefit Plans [Text Block]
Common share dividends
Dividends, Common Stock
Banking and Thrift, Interest [Abstract]
Interest on long-term debt
Interest Expense, Long-term Debt
Interest on short-term notes
Interest Expense, Short-term Borrowings
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
Noncontrolling Interest [Abstract]
Schedule of Movements in Noncontrolling Interest
Summary Of Noncontrolling Interest [Table Text Block]
Summary Of Noncontrolling Interest
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]
Defined Benefit Plans and Other Postretirement Benefit Plans [Axis]
Defined Benefit Plans and Other Postretirement Benefit Plans [Axis]
Defined Benefit Plan and Other Postretirement Benefit Plan [Domain]
Defined Benefit Plan and Other Postretirement Benefit Plan [Domain]
Post-Retirement and Post-Employment Benefits [Member]
Other Postretirement Benefit 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 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
Schedule of Financing Charges
Interest Income and Interest Expense Disclosure [Table Text Block]
Income Tax Disclosure [Abstract]
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.
Payables and Accruals [Abstract]
Accounts Payable and Other Current Liabilities
Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block]
Fair Value Disclosures [Abstract]
Fair Value Inputs Assets Liabilities Quantitative Information [Table]
Fair Value Inputs Assets Liabilities Quantitative Information [Table]
Fair value inputs assets liabilities quantitative information.
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, Hierarchy [Axis]
Fair Value, Hierarchy [Axis]
Fair Value Hierarchy [Domain]
Fair Value Hierarchy [Domain]
Level 1 [Member]
Fair Value, Inputs, Level 1 [Member]
Level 2 [Member]
Fair Value, Inputs, Level 2 [Member]
Level 3 [Member]
Fair Value, Inputs, Level 3 [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]
Liabilities:
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Bank indebtedness
Short-term Bank Loans and Notes Payable
Short-term notes payable
Commercial Paper
Long-term debt, including current portion, fair value
Long-term Debt, Fair Value
Fair value hedge - interest-rate swap
Derivative Liability, Noncurrent
Total liabilities, fair value
Financial Liabilities Fair Value Disclosure
Assets:
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents
Cash and Cash Equivalents, at Carrying Value
Total assets
Assets, Fair Value Disclosure
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]
Pension Benefits [Member]
Pension Plan [Member]
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 for Next Fiscal Year
Health care rate
Percentage Increase In Health Care Cost
Percentage increase in health care cost.
Health care cost trend rate
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate
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]
Derivative Instrument [Axis]
Derivative Instrument [Axis]
Derivative Contract [Domain]
Derivative Contract [Domain]
Interest Rate Swap [Member]
Interest Rate Swap [Member]
125 Fixed-to-Floating Interest-Rate Swap [Member]
One Twenty Five Million Fixed To Floating Interest Rate Swap [Member]
One twenty five million fixed to floating interest rate swap.
250 Fixed-to-Floating Interest-Rate Swap [Member]
Two Five Zero Million Fixed To Floating Interest Rate Swap [Member]
Two five zero million fixed to floating interest rate swap.
Long-term Debt, Type [Axis]
Long-term Debt, Type [Axis]
Long-term Debt, Type [Domain]
Long-term Debt, Type [Domain]
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
Fair value hedge exposure
Percentage Of Fair Value Hedge Exposure
Percentage Of Fair Value Hedge Exposure
Number of agreements
Number Of Agreements
Number Of Agreements
Conversion of debt
Debt Conversion, Original Debt, Amount
Long-term debt
Debt Instrument, Face Amount
Notional value
Derivative, Notional Amount
Statement of Financial Position [Abstract]
Long-term debt measured at fair value
Fair Value Of Hedged Debt
Fair value of hedged debt.
Debt Disclosure [Abstract]
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.
Summary of Long Term Debt Interest Payment Obligations
Schedule Of Long Term Debt Interest Payments [Table Text Block]
Schedule Of Long Term Debt Interest Payments
Accounting Policies [Abstract]
Accounting Policies [Table]
Accounting Policies [Table]
Accounting Policies [Table]
Legal Entity [Axis]
Legal Entity [Axis]
Entity [Domain]
Entity [Domain]
B2M Limited Partnership [Member]
Bruce to Milton Limited Partnership [Member]
Bruce to Milton Limited Partnership [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]
Hydro One Remote Communities [Member]
Hydro One Remote Communities [Member]
Hydro One Remote Communities [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]
2016 Subsequently Approved Updated Revenue Requirements [Member]
Two Thousand Sixteen Subsequently Approved Updated Revenue Requirement [Member]
2016 subsequently approved updated revenue requirements.
2017 Subsequently Approved Updated Revenue Requirement [Member]
Two Thousand Seventeen Subsequently Approved Updated Revenue Requirement [Member]
2017 Subsequently approved updated revenue requirement.
Accounting Policies [Line Items]
Accounting Policies [Line Items]
Accounting Policies [Line Items]
Ownership interest in related party
Noncontrolling Interest, Ownership Percentage by Parent
Transmission revenue requirement
Electrical Transmission Revenue Requirement
Electrical transmission revenue requirement.
Distribution revenue requirement
Electrical Distribution Revenue Requirement.
Electrical distribution revenue requirement.
Increase in basic rate, distribution and generation of electricity
Increase In Basic Rate On Distribution And Generation Of Electricity
Increase In Basic Rate On Distribution And Generation Of Electricity
Short-term investments original maturity
Short Term Investment Original Maturity Term Maximum
Cash equivalent short term investment original maturity term maximum.
Threshold probability for recognition
Uncertain Tax Position Recognition Threshold
Uncertain tax position recognition threshold.
Asset impairment charges
Asset Impairment Charges
Embedded derivatives
Embedded Derivative, Fair Value of Embedded Derivative, Net
Dividends
Dividend Disclosure [Text Block]
Dividend Disclosure [Text Block]
Income Statement [Abstract]
Revenues
Electric Revenue [Abstract]
Distribution (includes $279 related party revenues; 2016 – $160) (Note 26)
Electrical Distribution Revenue
Transmission (includes $1,526 related party revenues; 2016 – $1,556) (Note 26)
Electrical Transmission Revenue
Total revenues
Electric and Gas Revenue
Costs
Cost of Goods Sold, Electric [Abstract]
Purchased power (includes $1,594 related party costs; 2016 – $2,103) (Note 26)
Cost of Purchased Power
Operation, maintenance and administration (Note 26)
Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses
Depreciation and amortization (Note 5)
Utilities Operating Expense, Depreciation and Amortization
Total costs
Costs and Expenses
Income before financing charges and income taxes
Operating Income (Loss)
Financing charges (Note 6)
Income taxes (Note 7)
Income Tax Expense (Benefit)
Net income
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Other comprehensive income
Other Comprehensive Income (Loss), Net of Tax
Comprehensive income
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest
Net income attributable to:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest [Abstract]
Noncontrolling interest (Note 25)
Net Income (Loss) Attributable to Noncontrolling Interest
Common shareholder
Net Income (Loss) Available to Common Stockholders, Basic
Net income
Net Income (Loss) Attributable to Parent
Comprehensive income attributable to:
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Noncontrolling interest (Note 25)
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 23)
Earnings Per Share [Abstract]
Basic (in dollars per share)
Earnings Per Share, Basic
Diluted (in dollars per share)
Earnings Per Share, Diluted
Dividends per common share declared (Note 22) (in dollars per share)
Common Stock, Dividends, Per Share, Declared
Accounts payable
Accounts Payable, Current
Accrued liabilities
Accrued Liabilities, Current
Accrued interest
Interest Payable, Current
Regulatory liabilities (Note 12)
Regulatory Liability, Current
Total
Accounts Payable and Other Accrued Liabilities, Current
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]
Receivables [Abstract]
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts – beginning
Allowance for Doubtful Accounts Receivable, Current
Write-offs
Allowance for Doubtful Accounts Receivable, Write-offs
Additions to allowance for doubtful accounts
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)
Allowance for doubtful accounts – ending
Current income taxes
Current Income Tax Expense (Benefit)
Deferred income taxes
Deferred Income Tax Expense (Benefit)
Total income taxes
Effective income tax rate
Effective Income Tax Rate Reconciliation, Percent
Commitments and Contingencies Disclosure [Abstract]
Loss Contingencies [Table]
Loss Contingencies [Table]
Range [Axis]
Range [Axis]
Range [Domain]
Range [Domain]
Maximum [Member]
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingencies [Line Items]
Plaintiff sought value
Loss Contingency Plaintiff Sought Value
Loss contingency plaintiff sought value.
Payments made
Loss Contingency Accrual, Payments
Property, Plant and Equipment [Abstract]
Depreciation and Amortization
Depreciation And Amortization [Text Block]
Depreciation And Amortization [Text Block]
Pension Plans Postretirement And Other Employee Benefits [Table]
Pension Plans Postretirement And Other Employee Benefits [Table]
Pension Plans Postretirement And Other Employee Benefits [Table]
Balance Sheet Location [Axis]
Balance Sheet Location [Axis]
Balance Sheet Location [Domain]
Balance Sheet Location [Domain]
Other [Member]
Other Investments [Member]
Major Types of Debt and Equity Securities [Axis]
Major Types of Debt and Equity Securities [Axis]
Major Types of Debt and Equity Securities [Domain]
Major Types of Debt and Equity Securities [Domain]
Equity Securities [Member]
Equity Securities [Member]
Debt Securities [Member]
Debt Securities [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]
Target Allocation
Pension Plan Asset Percentage
Pension plan asset percentage.
Pension Plan Assets
Target Allocation Percentage
Target allocation percentage.
Statement of Stockholders' Equity [Abstract]
Statement [Table]
Statement [Table]
Equity Components [Axis]
Equity Components [Axis]
Equity Component [Domain]
Equity Component [Domain]
Common Shares [Member]
Common Stock [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 (Note 25) [Member]
Noncontrolling Interest [Member]
Statement [Line Items]
Statement [Line Items]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest
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.
Distributions to noncontrolling interest
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders
Dividends on common shares
Return of stated capital (Note 21)
Return Of Stated Capital On Issuance And Outstanding Common Shares
Return of stated capital on issuance and outstanding common shares.
Ending balance
Subsequent Events [Abstract]
Subsequent Event [Table]
Subsequent Event [Table]
Subsequent Event Type [Axis]
Subsequent Event Type [Axis]
Subsequent Event Type [Domain]
Subsequent Event Type [Domain]
Subsequent Event
Subsequent Event [Member]
Subsequent Event [Line Items]
Subsequent Event [Line Items]
Preferred share dividends
Dividends, Preferred Stock
Return of stated capital, total amount approved
Approved Return Of Stated Capital On Issuance And Outstanding Common Shares
Approved return of stated capital on issuance and outstanding common shares.
Assets
Assets [Abstract]
Current assets:
Assets, Current [Abstract]
Accounts receivable (Note 8)
Accounts Receivable, Net, Current
Due from related parties (Note 26)
Due from Related Parties, Current
Other current assets (Note 9)
Other Assets, Current
Total current assets
Assets, Current
Property, plant and equipment (Note 10)
Property, Plant and Equipment, Net
Other long-term assets:
Assets, Noncurrent [Abstract]
Regulatory assets (Note 12)
Regulatory Assets, Noncurrent
Deferred income tax assets (Note 7)
Deferred Income Tax Assets, Net
Intangible assets (Note 11)
Intangible Assets, Net (Excluding Goodwill)
Goodwill (Note 4)
Goodwill
Other assets
Other Assets, Noncurrent
Total other long-term assets
Assets, Noncurrent
Total assets
Assets
Liabilities
Liabilities [Abstract]
Current liabilities:
Liabilities, Current [Abstract]
Bank indebtedness
Loans Payable to Bank, Current
Short-term notes payable (Note 15)
Long-term debt payable within one year (Notes 15, 16)
Long-term Debt, Current Maturities
Accounts payable and other current liabilities (Note 13)
Due to related parties (Note 26)
Due to Related Parties, Current
Total current liabilities
Liabilities, Current
Long-term liabilities:
Liabilities, Noncurrent [Abstract]
Long-term debt (includes $541 measured at fair value; 2016 – $548) (Notes 15, 16)
Long-term Debt, Excluding Current Maturities
Regulatory liabilities (Note 12)
Regulatory Liability, Noncurrent
Deferred income tax liabilities (Note 7)
Deferred Income Tax Liabilities, Net
Other long-term liabilities (Note 14)
Other Liabilities, Noncurrent
Total Long-term liabilities
Liabilities, Noncurrent
Total liabilities
Liabilities
Contingencies and Commitments (Notes 28, 29)
Commitments and Contingencies
Subsequent Events (Note 31)
Subsequent Events
Subsequent Events
Preferred shares (Note 21)
Preferred Stock, Value, Issued
Noncontrolling interest subject to redemption (Note 25)
Redeemable Noncontrolling Interest, Equity, Carrying Amount
Equity
Common shares (Note 21)
Common Stock, Value, Outstanding
Retained earnings
Retained Earnings (Accumulated Deficit)
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss), Net of Tax
Hydro One shareholder’s equity
Stockholders' Equity Attributable to Parent
Noncontrolling interest (Note 25)
Stockholders' Equity Attributable to Noncontrolling Interest
Total equity
Total liabilities, preferred shares, noncontrolling interest subject to redemption and equity
Liabilities and Equity
Related Party Transactions [Abstract]
Schedule of Related Party Transactions, by Related Party [Table]
Schedule of Related Party Transactions, by Related Party [Table]
Hydro One Limited [Member]
Hydro One Limited [Member]
Hydro One Limited [Member]
Related Party Transaction [Axis]
Related Party Transaction [Axis]
Related Party Transaction [Domain]
Related Party Transaction [Domain]
Amounts Related To Electricity Rebates [Member]
Amounts Related To Electricity Rebates [Member]
Amounts Related To Electricity Rebates [Member]
Cost Recovery For Services Provided [Member]
Cost Recovery For Services Provided [Member]
Cost Recovery For Services Provided [Member]
Class of Stock [Axis]
Class of Stock [Axis]
Class of Stock [Domain]
Class of Stock [Domain]
Preferred Class B [Member]
Preferred Class B [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]
Hydro One Brampton [Member]
Hydro One Brampton [Member]
Hydro One Brampton [Member]
Hydro One Telecom [Member]
Hydro One Telecom [Member]
Hydro One Telecom [Member]
2587264 Ontario Inc. [Member]
2587264 Ontario Inc. [Member]
2587264 Ontario Inc. [Member]
Public Utility [Axis]
Public Utility [Axis]
Utility Plant [Domain]
Utility Plant [Domain]
Transmission [Member]
Electric Transmission [Member]
Income Statement Location [Axis]
Income Statement Location [Axis]
Income Statement Location [Domain]
Income Statement Location [Domain]
Operating Expense [Member]
Operating Expense [Member]
Capitalized Costs [Member]
Capitalized Costs [Member]
Capitalized Costs [Member]
Related Party Transaction [Line Items]
Related Party Transaction [Line Items]
Ownership percentage
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners
Power purchased
Revenues for transmission services
Related party transaction amount
Related Party Transaction, Amounts of Transaction
Distribution revenues related to rural rate protection
Electric Domestic Regulated Revenue
Distribution revenues related to the supply of electricity to remote northern communities
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 construction and equipment maintenance services
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.
Return of stated capital
Partners' Capital Account, Return of Capital
Dividends paid
Dividends
Stock-based compensation costs
Share-based Compensation
Services received
Technology Services Costs
Revenues for services provided
Technology Services Revenue
Promissory note issued and repaid
Proceeds from Notes Payable
Promissory note repaid
Repayments of Notes Payable
Interest paid
Interest Paid
Preferred shares issued (in shares)
Preferred Stock, Shares Issued
Proceeds from preferred shares issued
Proceeds from Issuance of Preferred Stock and Preference Stock
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]
Relationship to Entity [Domain]
Relationship to Entity [Domain]
Male [Member]
Male [Member]
Male [Member]
Female [Member]
Female [Member]
Female [Member]
Approximate life expectancy (in years) at particular age
Approximate Life Expectancy In years At Particular Age
Approximate life expectancy at particular age.
2018
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months
2019
Defined Benefit Plan, Expected Future Benefit Payments, Year Two
2020
Defined Benefit Plan, Expected Future Benefit Payments, Year Three
2021
Defined Benefit Plan, Expected Future Benefit Payments, Year Four
2022
Defined Benefit Plan, Expected Future Benefit Payments, Year Five
2023 through to 2027
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter
Total estimated future benefit payments through to 2027
Defined Benefit Plan Expected Future Benefit Payments
Defined benefit plan expected future benefit payments.
Business Acquisition [Axis]
Business Acquisition [Axis]
Business Acquisition, Acquiree [Domain]
Business Acquisition, Acquiree [Domain]
Other assets
Other Assets
Pension benefit liability (Note 18)
Defined Benefit Pension Plan, Liabilities, Noncurrent
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
Debt Instrument [Axis]
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
$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]
Long-term debt, face amount
Carrying value
Long-term Debt
Fair value
Subsequent Events
Subsequent Events [Text Block]
Noncontrolling Interest [Table]
Noncontrolling Interest [Table]
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]
Shareholders' Equity Class [Axis]
Shareholders' Equity Class [Axis]
Fair Value by Shareholders' Equity Class [Domain]
Fair Value by Shareholders' Equity Class [Domain]
Equity [Member]
Equity Issued in Business Combination [Member]
Financial Instrument [Axis]
Financial Instrument [Axis]
Financial Instruments [Domain]
Financial Instruments [Domain]
Debt [Member]
Debt [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest [Line Items]
Business combination assets transferred
Business Combination, Consideration Transferred
Business combination percentage transferred
Business Combination Consideration Transferred Percentage
Business combination consideration transferred percentage.
Percentage of common shares acquired
Business Acquisition, Percentage of Voting Interests Acquired
Business acquisition, consideration paid
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable
Capital units in initial investment
Capital Units, Net Amount
PBO
Defined Benefit Plan, Benefit Obligation
ABO
Defined Benefit Plan, Accumulated Benefit Obligation
Fair value of plan assets
Defined Benefit Plan, Fair Value of Plan Assets
Environmental Remediation Obligations [Abstract]
2018
Estimated Future Environmental Expenditures Due In One Year
Estimated future environmental expenditures due in one year.
2019
Estimated Future Environmental Expenditures Due In Two Years
Estimated future environmental expenditures due in two year.
2020
Estimated Future Environmental Expenditures Due In Three Years
Estimated future environmental expenditures due in three year.
2021
Estimated Future Environmental Expenditures Due In Four Years
Estimated future environmental expenditures due in four year.
2022
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.
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
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.
Operating lease commitments, year 1
Operating Leases, Future Minimum Payments Due, Next Twelve Months
Operating lease commitments, year 2
Operating Leases, Future Minimum Payments, Due in Two Years
Operating lease commitments, year 3
Operating Leases, Future Minimum Payments, Due in Three Years
Operating lease commitments, year 4
Operating Leases, Future Minimum Payments, Due in Four Years
Operating lease commitments, year 5
Operating Leases, Future Minimum Payments, Due in Five Years
Operating lease commitments, thereafter
Operating Leases, Future Minimum Payments, Due Thereafter
Schedule of Business Acquisitions, by Acquisition [Table]
Schedule of Business Acquisitions, by Acquisition [Table]
Orillia Power Distribution Corporation [Member]
Orillia Power Distribution Corporation [Member]
Orillia Power Distribution Corporation.
Business Acquisition [Line Items]
Business Acquisition [Line Items]
Purchase price of acquisition
Business Acquisition Purchase Price
Business Acquisition Purchase Price
Business acquisition, consideration outstanding indebtedness
Business Combination, Consideration Transferred, Liabilities Incurred
Goodwill
Adjustment to deferred tax liability
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Tax Liability
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Tax Liability
Revenues
Business Combination, Separately Recognized Transactions, Revenues and Gains Recognized
Net income
Business Combination, Separately Recognized Transactions, Net Gains and Losses
Noncontrolling Interest
Noncontrolling Interest Disclosure [Text Block]
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.
Regulated Operations [Abstract]
Summary of Company's Capital Structure
Schedule of Capitalization [Table Text Block]
Property, Plant and Equipment [Table]
Property, Plant and Equipment [Table]
Distribution [Member]
Electric Distribution [Member]
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, gross
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
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, Gross, Current
Allowance for doubtful accounts
Accounts receivable, net
Permissible limit on debt to total capital percentage
Debt Instrument Covenant Debt To Capital Percentage
Debt instrument covenant debt to capital percentage.
Business Combinations
Business Combination Disclosure [Text Block]
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets
Intangible Assets Disclosure [Text Block]
Employees Transfer [Member]
Employees Transfer [Member]
Employees transfer.
Change in projected benefit obligation
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, beginning of year
Current service cost
Defined Benefit Plan, Service Cost
Employee contributions
Defined Benefit Plan, Contributions by Plan Participants
Interest cost
Defined Benefit Plan, Interest Cost
Benefit paid
Defined Benefit Plan, Benefit Obligation, Benefits Paid
Defined Benefit Plan, Benefit Obligation, Benefits Paid
Net actuarial loss (gain)
Defined Benefit Plan, Actuarial Gain (Loss)
Change due to employees transfer
Defined Benefit Plan, Special Termination Benefits
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
Actual return on plan assets
Defined Benefit Plan, Actual Return on Plan Assets
Benefits paid
Defined Benefit Plan, Plan Assets, Benefits Paid
Defined Benefit Plan, Plan Assets, Benefits Paid
Employer contributions
Defined Benefit Plan, Contributions by Employer
Administrative expenses
Defined Benefit Plan, Administration Expenses
Fair value of plan assets, end of year
Unfunded status
Defined Benefit Plan, Funded Status of Plan
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]
Lar [Member]
LAR [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 balance
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 balance
Less: current portion
Environmental Liabilities Current Portion
Environmental liabilities current portion.
Environmental liabilities non current portion
Environment Liabilities Non Current
Environment liabilities non current.
Minimum [Member]
Minimum [Member]
Long-term inflation rate assumption of current costs
Inflation Rate
Inflation rate.
Future environmental expenditure discount rate
Accrual for Environmental Loss Contingencies, Discount Rate
Undiscounted environmental liabilities
Environmental Liabilities Undiscounted Basis
Environmental liabilities undiscounted basis.
Increase (decrease) of environmental liability due to revaluation adjustment
Schedule of Accounts Payable and Other Current Liabilities
Schedule of Accounts Payable and Accrued Liabilities [Table Text Block]
Undiscounted environmental liabilities
Less: discounting environmental liabilities to present value
Accrued Discount Liability
Accrued discount liability.
Discounted environmental liabilities
Environmental Liabilities Discounted Basis
Environmental liabilities discounted basis.
Summary of Related Party Transactions
Related Party Transactions Details [Table Text Block]
Related party transactions details table.
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]
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Regulatory assets (Note 12)
Regulatory Assets, Current
Materials and supplies
Inventory, Raw Materials and Supplies, Gross
Prepaid expenses and other assets
Prepaid Expense and Other Assets, Current
Other current assets
Significant Accounting Policies
Significant Accounting Policies [Text Block]
Schedule of Property, Plant and Equipment
Property, Plant and Equipment [Table Text Block]
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Plan Name [Axis]
Plan Name [Axis]
Plan Name [Domain]
Plan Name [Domain]
PWU Share Grant Plan [Member]
PWU Share Grant Plan [Member]
PWU Share Grant Plan [Member]
Society Share Grant Plan [Member]
Society Share Grant Plan [Member]
Society Share Grant Plan [Member]
Share Grant Plans [Member]
Share Grant Plans [Member]
Share Grant Plans [Member]
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]
Long Term Incentive Plan [Member]
Long Term Incentive Plan [Member]
Long Term Incentive 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]
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]
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
Weighted-average 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
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)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross
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.
Compensation expenses
Allocated Share-based Compensation Expense
Liability related to outstanding DSUs
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
Defined Contribution Plan, 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
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
Share-based Compensation Arrangement By Share-based Payment Award, Non-Option Equity Based Instruments, Value Equivalent To Common Shares
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]
Rate Setting
Revenue Recognition, Retrospective Rate-Setting Systems, 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 Recognition, Policy [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 Compensation, Option and Incentive Plans Policy [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 Obligations, Policy [Policy Text Block]
New Accounting Pronouncements
New Accounting Pronouncements, Policy [Policy Text Block]
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]
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.
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-term Debt Instruments [Table]
Credit Facility [Axis]
Credit Facility [Axis]
Credit Facility [Domain]
Credit Facility [Domain]
Commercial Paper Program [Member]
Commercial Paper [Member]
Revolving Credit Facility [Member]
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument [Line Items]
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
Maximum borrowing capacity
Line of Credit Facility, Maximum Borrowing Capacity
Fair Value of Financial Instruments and Risk Management
Fair Value Disclosures [Text Block]
Property, Plant and Equipment
Property, Plant and Equipment Disclosure [Text Block]
Capital Management
Capital Structure Disclosure [Text Block]
Capital Structure Disclosure [Text Block]
Fair Value Of Financial Instruments [Table]
Fair Value Of Financial Instruments [Table]
Fair Value Of Financial Instruments [Table]
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
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.
Schedule of Intangible Assets
Schedule of Finite-Lived Intangible Assets [Table Text Block]
Long-term:
Non Current Deferred Income Taxes [Abstract]
Non current deferred income taxes.
Deferred income tax assets
Deferred Tax Assets, Gross, Noncurrent
Deferred income tax liabilities
Deferred Tax Liabilities, Gross, Noncurrent
Net deferred income tax assets
Deferred Tax Assets, Net
Debt and Credit Agreements
Debt Disclosure [Text Block]
Schedule of Defined Benefit Plans Disclosures [Table]
Schedule of Defined Benefit Plans Disclosures [Table]
Defined Benefit Plan, Asset Categories [Axis]
Defined Benefit Plan, Asset Categories [Axis]
Plan Asset Categories [Domain]
Plan Asset Categories [Domain]
Pooled Funds [Member]
Pooled Funds [Member]
Pooled Funds [Member]
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Member]
Short-term Securities [Member]
Money Market Funds [Member]
Derivative instruments [Member]
Derivative [Member]
Corporate Shares - Canadian [Member]
Domestic Corporate Debt Securities [Member]
Corporate Shares - Foreign [Member]
Foreign Corporate Debt Securities [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 Disclosure [Line Items]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets
Pension Plan Assets Measured At Fair Value
Pension plan assets 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.
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.
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.
Income Taxes
Income Tax Disclosure [Text Block]
Cash and cash equivalents
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents
Property, plant and equipment
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment
Intangible assets
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill
Regulatory assets
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Regulatory Assets
Business combination recognized identifiable assets acquired and liabilities assumed regulatory assets.
Working capital
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Working Capital
Business combination recognized identifiable assets acquired and liabilities assumed working capital.
Long-term debt
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt
Pension and post-employment benefit liabilities, net
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Pension and Post-Employment Benefit Liabilities Net
Business combination recognized identifiable assets acquired and liabilities assumed pension and post-employment benefit liabilities net.
Deferred income taxes
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent
Total
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net
Segment Reporting [Abstract]
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.
Asset Retirement Obligation Disclosure [Abstract]
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.
Asset retirement obligations recorded
Asset Retirement Obligation
Schedule Of Regulatory Assets And Liabilities [Table]
Schedule Of Regulatory Assets And Liabilities [Table]
Schedule Of Regulatory Assets And Liabilities [Table]
Regulatory Liability [Axis]
Regulatory Liability [Axis]
Regulatory Liability [Domain]
Regulatory Liability [Domain]
Green Energy Expenditure Variance [Member]
Green Energy expenditure variance [Member]
Green Energy expenditure variance [Member]
External Revenue Variance [Member]
External Revenue Variance [Member]
External Revenue Variance [Member]
CDM Deferral Variance [Member]
Conservation And Demand Management Deferral Variance Account [Member]
Conservation And Demand Management Deferral Variance Account [Member]
Pension Cost Variance [Member]
Pension Cost Variance [Member]
Pension Cost Variance [Member]
2015 - 2017 Rate Rider [Member]
Two Thousand Fifteen To Two Thousand Seventeen Rate Rider [Member]
Two Thousand Fifteen To Two Thousand Seventeen Rate Rider [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]
Regulatory Asset [Axis]
Regulatory Asset [Axis]
Regulatory Asset [Domain]
Regulatory Asset [Domain]
Deferred Income Tax Charge [Member]
Deferred Income Tax Charge [Member]
Pension Benefit Regulatory Asset [Member]
Pension Costs [Member]
Post-Retirement and Post-Employment Benefits [Member]
Postretirement Benefit Costs [Member]
Environmental [Member]
Environmental Restoration Costs [Member]
Share-Based Compensation [Member]
Share Based Compensation [Member]
Share Based Compensation [Member]
Debt Premium [Member]
Debt Premium [Member]
Debt Premium [Member]
Foregone Revenue Deferral [Member]
Foregone Revenue Deferral [Member]
Foregone Revenue Deferral [Member]
Distribution System Code Exemption [Member]
Distribution System Code Exemption [Member]
Distribution system code exemption.
B2M LP Start-Up Costs [Member]
Bruce to Milton Limited Partnership Start Up Costs [Member]
Bruce to Milton Limited Partnership Start Up Costs [Member]
Retail Settlement Variance Account [Member]
Retail Settlement Variance Accounts [Member]
Retail settlement variance accounts.
Other Regulatory Assets [Member]
Other Regulatory Assets [Member]
Other Regulatory Assets [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
Schedule of Stock by Class [Table]
Schedule of Stock by Class [Table]
Preferred Class A [Member]
Preferred Class A [Member]
Class of Stock [Line Items]
Class of Stock [Line Items]
Common shares, issued and outstanding (in shares)
Common Shares Issued And Outstanding
Common shares issued and outstanding.
Return of stated capital, total amount paid
Number of series of preferred stock (in series)
Number Of Series Of Preferred Stock
Number Of Series Of Preferred Stock
Preferred dividend rate, basis spread on variable rate
Preferred Stock, Dividend Rate, Basis Spread On Variable Rate
Preferred Stock, Dividend Rate, Basis Spread On Variable Rate
Preferred shares outstanding (in shares)
Preferred Stock, Shares Outstanding
Preferred shares issued
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
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]
Revenues
Electric Revenue
Purchased power
Operation, maintenance and administration
Depreciation and amortization
Depreciation, Depletion and Amortization, Nonproduction
Capital investments
Payments to Acquire Productive Assets
Total assets
Related Party [Member]
Related Party [Member]
Related Party [Member]
Distribution revenues
Transmission revenues
Purchased power costs
Supplemental Cash Flow Information [Abstract]
Capital contribution received
Capital Contributions Received
Capital contributions received.
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 Temporary Equity Carrying Amount
Redeemable Noncontrolling Interest Temporary Equity Carrying Amount
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
Distributions to noncontrolling interest, equity
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
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
Noncontrolling interest - ending balance
Accounting Changes and Error Corrections [Abstract]
Schedule of Accounting Standards Updates Issued by Financial Accounting Standards Board
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]
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
Commitments [Table]
Commitments [Table]
Commitments [Table]
Other Commitments [Axis]
Other Commitments [Axis]
Other Commitments [Domain]
Other Commitments [Domain]
Long-Term Software/Meter Agreement [Member]
Long Term Software And Meter Agreement [Member]
Long term software and meter agreement.
Operating Leases [Member]
Operating Leases [Member]
Operating leases.
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
Lessee Leasing Arrangements, Operating Leases, Term of Contract
Operating lease renewal options
Lessee Leasing Arrangements, Operating Leases, Renewal Term
Lease payments
Operating Lease Payments
Operating Lease Payments
Financing Charges
Interest Income and Interest Expense Disclosure [Text Block]
Market Risk Credit Risk And Liquidity Risk [Table]
Market Risk Credit Risk And Liquidity Risk [Table]
Market Risk Credit Risk And Liquidity Risk [Table]
Financing Receivables, Period Past Due [Axis]
Financing Receivables, Period Past Due [Axis]
Financing Receivables, Period Past Due [Domain]
Financing Receivables, 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]
Trading Activity [Axis]
Trading Activity [Axis]
Trading Activity, by Type [Domain]
Trading Activity, by Type [Domain]
Variable Interest Rate [Member]
Variable Interest Rate [Member]
Variable Interest Rate [Member]
Concentration Risk Type [Axis]
Concentration Risk Type [Axis]
Concentration Risk Type [Domain]
Concentration Risk Type [Domain]
Customer Concentration Risk [Member]
Customer Concentration Risk [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]
Impact on net income
Impact Of One Percent Change In Yield For Results Of Operations
Impact of one percent change in yield for results of operations.
Accounts receivable
Accounts Receivable, Net
Provision for bad debts
Account receivable, percentage
Account Receivable Net Percentage
Account Receivable Net Percentage
Account receivable, period
Accounts Receivable Collection Period
Accounts Receivable Collection Period
Statutory income tax rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
Income taxes at statutory rate of 26.5% (2016 - 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
Pension contributions in excess of pension expense
Pension Contributions in Excess of Pension Expense
Pension Contributions in Excess of Pension Expense
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
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 permanent differences
Net Permanent Differences Reconciliation
Net Permanent Differences Reconciliation
Other Current Assets
Other Current Assets [Text Block]
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]
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 rate of amortization, intangible assets
Amortization Rate on Intangible Assets
Amortization Rate on Intangible Assets
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.
Earnings Per Common Share
Earnings Per Share [Text Block]
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 vested and issued (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)
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)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Weighted-average price, vested and issued (in dollars per share)
Weighted-average 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, ending (in dollars per share)
Depreciation of property, plant and equipment
Depreciation
Asset removal costs
Amortization Of Capitalized Asset Retirement Obligation Costs
The amortization of the asset retirement obligation costs that got capitalized.
Amortization of intangible assets
Amortization of Intangible Assets
Amortization of regulatory assets
Amortization of Regulatory Asset
Total depreciation and amortization
Summary of Commitments Under Leases, Outsourcing and Other Agreements Due
Contractual Obligation, Fiscal Year Maturity Schedule [Table Text Block]
Summary of Other Commitments
Other Commitments [Table Text Block]
Schedule of Consolidated Statement of Cash Flows
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]
Accounts Receivable
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]
Other Liabilities Disclosure [Abstract]
Post-retirement and post-employment benefit liability (Note 18)
Postretirement And Postemployment Benefit Plans Liabilities Non Current
Postretirement and postemployment benefit plans liabilities non current.
Environmental liabilities (Note 19)
Accrued Environmental Loss Contingencies, Noncurrent
Due to related parties (Note 26)
Due to Related Parties, Noncurrent
Asset retirement obligations (Note 20)
Asset Retirement Obligations, Noncurrent
Long-term accounts payable and other liabilities
Accounts Payable and Accrued Liabilities, Noncurrent
Total
Regulatory Matters [Table]
Regulatory Matters [Table]
Regulatory Matters [Table]
Deferred Income Tax Charge, Transmission Rate, 2017 And 2018 [Member]
Deferred Income Tax Charge, Transmission Rate, 2017 And 2018 [Member]
Deferred Income Tax Charge, Transmission Rate, 2017 And 2018 [Member]
Deferred Income Tax Charge, Transmission Rate, 2018-2022 [Member]
Deferred Income Tax Charge, Transmission Rate, 2018-2022 [Member]
Deferred Income Tax Charge, Transmission Rate, 2018-2022 [Member]
Polychlorinated Biphenyl Liability [Member]
Polychlorinated Biphenyl Liability [Member]
Polychlorinated Biphenyl Liability [Member]
Land Assessment and Remediation Liability [Member]
Land Assessment And Remediation [Member]
Land Assessment And Remediation [Member]
Environmental Expenditure [Member]
Environmental [Member]
Environmental [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.
Pending amount of impairment to regulatory assets
Amount of Impairment to Carrying Amount of Regulatory Assets, Pending Amount
Amount of Impairment to Carrying Amount of Regulatory Assets, Pending Amount
Increase (decrease) in other comprehensive income
Increase Decrease In Other Comprehensive Income One
Increase (decrease) in other comprehensive income one attributable to regulated accounting.
Regulatory asset increase (decrease)
Increase Decrease To Regulatory Assets
Increase (decrease) to regulatory assets.
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 amortization expense
Increase Decrease In Amortization Expense
Increase (decrease) in amortization expense 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.
Approved recovery start up costs
Approved Recovery Of Initial Start Up Costs
Approved recovery of initial start up costs.
Start up costs recovery period
Start Up Costs Recovery Period
Start up costs recovery period.
Disposal period of approved balances for disposition
Disposal Period Of Approved Balances For Disposition
Disposal Period Of Approved Balances For Disposition
Increase (decrease) in revenue
Increase Decrease In Revenue
Increase (decrease) in revenue attributable to regulatory accounting.
Summary of Share Grant Activity
Schedule of Share-based Compensation, Stock Options, 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
Contingencies
Contingencies Disclosure [Text Block]
New Accounting Pronouncements
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]
Related Party Transactions
Related Party Transactions Disclosure [Text Block]
Weighted average number of shares outstanding (in shares)
Weighted Average Number of Shares Outstanding, Basic
Dilutive securities (in shares)
Weighted Average Number Diluted Shares Outstanding Adjustment
Long-term debt payable within one year
Less: cash and cash equivalents
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
Preferred shares (Note 21)
Common shares
Total capital
Capitalization, Long-term Debt and Equity
Other Long-Term Liabilities
Other Liabilities Disclosure [Text Block]
2018 [Member]
Debt Instrument Maturity Period Year One [Member]
Debt Instrument Maturity Period Year One [Member]
2019 [Member]
Debt Instrument Maturity Period Year Two [Member]
Debt Instrument Maturity Period Year Two [Member]
2020 [Member]
Debt Instrument Maturity Period Year Three [Member]
Debt Instrument Maturity Period Year Three [Member]
2021 [Member]
Debt Instrument Maturity Period Year Four [Member]
Debt Instrument Maturity Period Year Four [Member]
2022 [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]
2023-2027 [Member ]
Debt Instrument Maturity Period Between Six To Ten Years [Member ]
Debt Instrument Maturity Period Between Six To Ten Years [Member ]
2028 [Member]
Debt Instrument Maturity Period Over Ten Years [Member]
Debt Instrument Maturity Period Over Ten Years [Member]
Interest payments
Interest Expense, Debt
Segmented Reporting
Segment Reporting Disclosure [Text Block]
Stock-Based Compensation
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]
Consolidated Statements of Cash Flows
Cash Flow, Supplemental Disclosures [Text Block]
Regulatory Assets and Liabilities
Schedule of Regulatory Assets and Liabilities [Text Block]
Schedule of Other Long-Term Liabilities
Other Noncurrent Liabilities [Table Text Block]
Long-term debt, noncurrent
Total long-term debt
5.18% Series 13 Notes Due 2017 [Member]
Five Point Eighteen Percent Series Thirteen Notes Due Two Thousand Seventeen [Member]
Five Point Eighteen Percent Series Thirteen Notes Due Two Thousand Seventeen [Member]
2.78% Series 28 Notes Due 2018 [Member]
Two Point Seventy Eight Percent Series Twenty Eight Notes Due Two Thousand Eighteen [Member]
Two Point Seventy Eight Percent Series Twenty Eight Notes Due Two Thousand Eighteen [Member]
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.
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]
2.77% 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.
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.
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: Deferred debt issuance costs
Debt Issuance Costs, Current, Net
Total long-term debt
Long-term debt, interest rate
Debt Instrument, Interest Rate, Stated Percentage
Hedged portion of debt
Hedged Portion of Long-Term Debt
Hedged portion of long-term debt.
Unrealized mark-to-market gain (loss)
Unrealized Gain Loss On Debt Interest Rate Swaps
Unrealized gain loss on debt interest rate swaps.
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
Summary of Segment Information
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Commitments
Commitments Disclosure [Text Block]
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
Other Commitments [Table]
Other Commitments [Table]
Credit Facilities [Member]
Credit Facilities [Member]
Credit Facilities [Member]
Letters Of Credit [Member]
Letter of Credit [Member]
Guarantees [Member]
Guarantees [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 1
Other Commitment, Due in Next Twelve Months
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
Other commitment
Other Commitment
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]
Schedule of Depreciation and Amortization
Schedule Of Depreciation And Amortization [Table Text Block]
Schedule Of Depreciation And Amortization
Actuarial loss
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.
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 on Plan Assets
Amortization of actuarial losses
Defined Benefit Plan, Amortization of Gains (Losses)
Net periodic benefit costs
Defined Benefit Plan, Net Periodic Benefit Cost
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.
Asset Retirement Obligations
Asset Retirement Obligation Disclosure [Text Block]
1 Year [Member]
2 Years [Member]
3 Years [Member]
4 Years [Member]
5 Years [Member]
5 Years, Total [Member]
6-10 Years [Member ]
Over 10 Years [Member]
1 year
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months
2 years
Long-term Debt, Maturities, Repayments of Principal in Year Two
3 years
Long-term Debt, Maturities, Repayments of Principal in Year Three
4 years
Long-term Debt, Maturities, Repayments of Principal in Year Four
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
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.
Over 10 years
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
Weighted average interest rate
Debt, Weighted Average Interest Rate
Award Type [Axis]
Award Type [Axis]
Equity Award [Domain]
Equity Award [Domain]
Number of PSUs [Member]
Performance Share Units [Member]
Performance share units.
Number of 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
Units granted (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Units vested (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period
Units forfeited (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Units outstanding - ending (in shares)
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.
Environmental Liabilities
Environmental Liabilities Disclosure [Text Block]
Environmental Liabilities Disclosure [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
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.
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
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 paid (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised
DSUs outstanding - December 31 (in shares)
Statement of Cash Flows [Abstract]
Operating activities
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income
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 (excluding asset removal costs)
Depreciation, Depletion and Amortization
Regulatory assets and liabilities
Increase (Decrease) in Regulatory Assets and Liabilities
Deferred income taxes
Other
Other Operating Activities, Cash Flow Statement
Changes in non-cash balances related to operations (Note 27)
Increase (Decrease) in Operating Capital
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
Promissory note issued (Note 26)
Promissory note repaid (Note 26)
Return of stated capital
Repayment Of Stated Capital
Repayment of stated capital.
Dividends paid
Payments of Dividends
Distributions paid to noncontrolling interest
Payments to Noncontrolling Interests
Change in bank indebtedness
Proceeds from (Repayments of) Bank Overdrafts
Other
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
Payments to Acquire Property, Plant, and Equipment
Intangible assets
Payments to Acquire Intangible Assets
Acquisitions (Note 4)
Payments to Acquire Businesses, Net of Cash Acquired
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 and Cash Equivalents, Period Increase (Decrease)
Cash and cash equivalents, beginning of year
Cash and cash equivalents, end of year
Accounts receivable
Increase (Decrease) in Accounts Receivable
Due from related parties
Increase (Decrease) in Due from Related Parties, Current
Materials and supplies
Increase (Decrease) in Materials and Supplies
Prepaid expenses and other assets
Increase (Decrease) in Prepaid Expense and Other 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
Capital Expenditure [Abstract]
Capital Expenditure [Abstract]
Capital Expenditure [Abstract]
Capital investments in property, plant and equipment
Capital Investments In Property Plant And Equipment
Capital Investments In 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
Capitalized Depreciation And Net Change In Accruals Included In Capital Investments In Property Plant And Equipment
Cash outflow for capital expenditures – property, plant and equipment
Capital investments in intangible assets
Capital Investments In Intangible Assets
Capital Investments In Intangible Assets
Net change in accruals included in capital investments in intangible assets
Net Change In Accruals Included In Capital Investments In Intangible Assets
Net Change In Accruals Included In Capital Investments In Intangible Assets
Cash outflow for capital expenditures – intangible assets
Net interest paid
Interest Paid, Net
Income taxes paid
Income Taxes Paid
Schedule of Regulatory Assets and Liabilities
Schedule Of Regulatory Assets And Liabilities [Table Text Block]
Schedule Of Regulatory Assets And Liabilities [Table Text Block]
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]
ABO [Member]
Accumulated Benefit Obligation [Member]
Accumulated Benefit Obligation [Member]
PBO [Member]
Projected Benefit Obligation [Member]
Projected Benefit Obligation [Member]
Defined Contribution Plan Name [Axis]
Defined Contribution Plan Name [Axis]
Defined Contribution Plan Name [Domain]
Defined Contribution 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]
Defined Contribution Pension Plan [Member]
Defined Contribution Pension Plan [Member]
Defined contribution pension plan.
Percentage of employer matching contribution
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 2018
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year
Estimated annual pension plan contributions for 2019
Defined Benefit Plans Estimated Future Employer Contributions In Year Two
Defined Benefit Plans Estimated Future Employer Contributions In Year Two
Funded percentage
Defined Benefit Plan, Funded Percentage
Pension plan
Defined Benefit Plan, Amount of Employer and Related Party Securities Included in Plan Assets
Percentage of assets to ascertain concentration of credit risk
Percent of Assets to Phase in for Determining Risk Weighted Assets
Percentage of assets to ascertain concentration of credit risk.
Deferred income tax assets
Deferred Tax Assets, Gross [Abstract]
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.
Non-depreciable capital property
Deferred Tax Assets Non Depreciable Capital Property
Deferred tax assets non depreciable capital property.
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
Environmental expenditures
Deferred Tax Assets Environmental Reserve
Deferred Tax Assets Environmental Reserve
Non-capital losses
Deferred Tax Assets Non Capital Losses
Deferred tax assets non capital losses.
Tax credit carryforwards
Deferred Tax Assets, Tax Credit Carryforwards
Investment in subsidiaries
Deferred Tax Assets, Investment in Subsidiaries
Other
Deferred Tax Assets, Other
Deferred income tax assets gross
Deferred Tax Assets, Gross
Less: valuation allowance
Deferred Tax Assets, Valuation Allowance
Total deferred income tax assets
Deferred Tax Assets, Net of Valuation Allowance
Less: current portion
Deferred Tax Assets, Net of Valuation Allowance, Current
Deferred income tax assets, noncurrent
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent
Deferred income tax liabilities
Deferred Tax Liabilities, Gross [Abstract]
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
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
Other
Deferred Tax Liabilities, Other
Total deferred income tax liabilities
Deferred Tax Liabilities, Net
Less: current portion
Deferred Tax Liabilities, Net, Current
Deferred income tax liabilities, noncurrent
Deferred Tax Liabilities, Net, Noncurrent
Valuation allowance in respect of capital property
Description of the Business
Business Description and Basis of Presentation [Text Block]
Schedule of Other Current Assets
Schedule of Other Current Assets [Table 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, 2018
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months
Amortization expense for intangible assets, 2019
Finite-Lived Intangible Assets, Amortization Expense, Year Two
Amortization expense for intangible assets, 2020
Finite-Lived Intangible Assets, Amortization Expense, Year Three
Amortization expense for intangible assets, 2021
Finite-Lived Intangible Assets, Amortization Expense, Year Four
Amortization expense for intangible assets, 2022
Finite-Lived Intangible Assets, Amortization Expense, Year Five
Financing charges capitalized on property, plant and equipment
Allowance for Funds Used During Construction, Capitalized Interest