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Summary of Significant Accounting Policies - Revisions to Prior Periods (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Summary Of Significant Accounting Policies [Line Items]      
Gross Sales $ 48,811 $ 13,914 [1] $ 21,715 [1]
Purchased Product $ 23,481 5,681 [1] 8,789 [1]
Oil Sands      
Disclosure Of Summary Of Significant Accounting Policies [Line Items]      
Gross Sales   8,804 13,101
Purchased Product   1,262 2,231
Gross sales less purchased product   7,542 10,870
Previously Reported | Oil Sands      
Disclosure Of Summary Of Significant Accounting Policies [Line Items]      
Gross Sales   8,481 12,739
Purchased Product   939 1,869
Gross sales less purchased product   7,542 10,870
Revision | Oil Sands      
Disclosure Of Summary Of Significant Accounting Policies [Line Items]      
Gross Sales   323 362
Purchased Product   323 362
Gross sales less purchased product   $ 0 $ 0
[1] See Note 3(w) for revisions to comparative results.