Changes in Accumulated other comprehensive income ("AOCI") by component (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 41,492
Other comprehensive income before reclassifications	685	$ (24)
Amounts reclassified from AOCI	10	7
Net other comprehensive income	695	(17)
Ending balance	42,819
Accumulated other comprehensive Income (loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(618)	91
Ending balance	77	74
Foreign currency net of hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	837	1,505
Other comprehensive income before reclassifications	685	(27)
Amounts reclassified from AOCI	0	0
Net other comprehensive income	685	(27)
Ending balance	1,522	1,478
Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	5	0
Other comprehensive income before reclassifications	0	0
Amounts reclassified from AOCI	1	1
Net other comprehensive income	1	1
Ending balance	6	1
Pension and post- retirement defined benefit plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,463)	(1,410)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from AOCI	9	6
Net other comprehensive income	9	6
Ending balance	(1,454)	(1,404)
Equity accounted investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3	(4)
Other comprehensive income before reclassifications	0	3
Amounts reclassified from AOCI	0	0
Net other comprehensive income	0	3
Ending balance	$ 3	$ (1)