Other comprehensive income (loss) and accumulated other comprehensive loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	$ (2,103)	$ (2,814)
Other comprehensive income (loss) before reclassifications	2,238	548
Amounts reclassified from accumulated other comprehensive loss	(44)	163
Net other comprehensive income (loss)	2,194	711
AOC Income (Loss), Ending balance	91	(2,103)
Foreign currency net of hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(182)	112
Other comprehensive income (loss) before reclassifications	1,687	(294)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net other comprehensive income (loss)	1,687	(294)
AOC Income (Loss), Ending balance	1,505	(182)
Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(4)	(40)
Other comprehensive income (loss) before reclassifications	0	28
Amounts reclassified from accumulated other comprehensive loss	4	8
Net other comprehensive income (loss)	4	36
AOC Income (Loss), Ending balance	0	(4)
Pension and post-retirement defined benefit plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(1,915)	(2,878)
Other comprehensive income (loss) before reclassifications	387	808
Amounts reclassified from accumulated other comprehensive loss	118	155
Net other comprehensive income (loss)	505	963
AOC Income (Loss), Ending balance	(1,410)	(1,915)
Equity accounted investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(2)	(8)
Other comprehensive income (loss) before reclassifications	164	6
Amounts reclassified from accumulated other comprehensive loss	(166)	0
Net other comprehensive income (loss)	(2)	6
AOC Income (Loss), Ending balance	$ (4)	$ (2)