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Risk Management Activities - Impact of hedged items designated in hedging relationships on OCI and net earnings (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about hedging instruments [line items]      
Gains (losses) on cash flow hedges, before tax $ (255) $ 28 $ 77
Losses recognized in other comprehensive earnings (8) (141) (53)
Gain (loss) on hedge ineffectiveness recognised in profit or loss 0 0 0
Commodity contracts      
Disclosure of detailed information about hedging instruments [line items]      
Gains (losses) on cash flow hedges, before tax (268) 41 77
Commodity contracts | Revenue      
Disclosure of detailed information about hedging instruments [line items]      
Losses recognized in other comprehensive earnings (13) (137) (59)
Gain (loss) on hedge ineffectiveness recognised in profit or loss 0 0 0
Foreign exchange forwards on project hedges      
Disclosure of detailed information about hedging instruments [line items]      
Gains (losses) on cash flow hedges, before tax 0 (1)  
Foreign exchange forwards on project hedges | Property, plant and equipment      
Disclosure of detailed information about hedging instruments [line items]      
Losses recognized in other comprehensive earnings 1 0  
Gain (loss) on hedge ineffectiveness recognised in profit or loss 0 0  
Forward starting interest rate swaps      
Disclosure of detailed information about hedging instruments [line items]      
Gains (losses) on cash flow hedges, before tax 13 (12) 0
Forward starting interest rate swaps | Interest expense      
Disclosure of detailed information about hedging instruments [line items]      
Losses recognized in other comprehensive earnings 4 (4) 6
Gain (loss) on hedge ineffectiveness recognised in profit or loss $ 0 $ 0 $ 0