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Inventory Change in Inventory (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Oil and Gas, Average Sale Price and Production Cost Per Unit [Line Items]    
Inventories at the beginning of the period $ 238 $ 251
Net additions (use) 22 26
Write-downs 28 0
Change in foreign exchange rates 0 (2)
Inventories at the end of the period 167 238
Coal    
Oil and Gas, Average Sale Price and Production Cost Per Unit [Line Items]    
Write-downs $ 65 $ 37