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Risk Management Activities - Effect of Hedges (Details)
MWh in Millions, $ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2021
CAD ($)
Dec. 31, 2020
CAD ($)
Dec. 31, 2021
USD ($)
MWh
Dec. 31, 2021
CAD ($)
MWh
Dec. 31, 2020
USD ($)
MWh
Dec. 31, 2020
CAD ($)
MWh
Disclosure of detailed information about hedging instruments [line items]            
Hedging instrument, assets       $ 2   $ 2
Physical power sales | Cash flow hedges | Commodity risk management            
Disclosure of detailed information about hedging instruments [line items]            
Notional amount purchased | MWh     13 13 16 16
Hedging instrument, assets       $ 285   $ 573
Gain (loss) on hedge ineffectiveness $ (181) $ (33)        
Interest rate swap | Cash flow hedges | Interest rate risk | U.S. Dollars            
Disclosure of detailed information about hedging instruments [line items]            
Notional amount     $ 300   $ 150  
Gain (loss) on hedge ineffectiveness 3 3        
Hedging instrument, liabilities       3   (3)
Interest rate swap | Cash flow hedges | Interest rate risk | Canada, Dollars            
Disclosure of detailed information about hedging instruments [line items]            
Notional amount           75
Gain (loss) on hedge ineffectiveness   4        
Hedging instrument, liabilities           (4)
Foreign-denominated debt | Net Investment Hedge | Currency risk            
Disclosure of detailed information about hedging instruments [line items]            
Hedging instrument, assets       $ 473   $ 472
Gain (loss) on hedge ineffectiveness $ 0 $ 11        
Foreign-denominated debt | Net Investment Hedge | Currency risk | U.S. Dollars            
Disclosure of detailed information about hedging instruments [line items]            
Notional amount     $ 370   $ 370