Miscellaneous financial information - Narrative (Detail) - CAD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Additional Financial Information [Line Items]
Effect of LIFO inventory liquidation on income (loss)		$ (62)	$ 13	$ 19
Difference between LIFO carrying values and replacement cost of inventories		2,000	1,800
Inventory write-down		74
Inventory adjustments, before tax		82
Out of period impact of the inventory write down		57
Out of period impact of the inventory write down, Adjustment before tax		63
Research and development costs charged to expenses		74	89	105
Accounts payable and accrued liabilities included accrued taxes other than income taxes		$ 458	$ 415
Production and Manufacturing | Canada Emergency Wage Subsidy (CEWS)
Additional Financial Information [Line Items]
Amount received as part of the federal government subsidy program				$ 155
Upstream
Additional Financial Information [Line Items]
Non-cash impairment of goodwill	$ 20