Changes in Accumulated Other Comprehensive Loss ("AOCL") by Component - Changes in Accumulated Other Comprehensive Loss (AOCL) by Component (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	$ (1,539)	$ (2,791)	$ (2,103)	$ (2,814)
Other comprehensive income (loss) before reclassifications	1,641	107	2,143	48
Amounts reclassified from accumulated other comprehensive loss	31	41	93	123
Net other comprehensive (loss) income	1,672	148	2,236	171
AOC Income (Loss), Closing balance	133	(2,643)	133	(2,643)
Foreign currency net of hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	217	110	(182)	112
Other comprehensive income (loss) before reclassifications	1,618	6	2,017	4
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net other comprehensive (loss) income	1,618	6	2,017	4
AOC Income (Loss), Closing balance	1,835	116	1,835	116
Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(2)	(91)	(4)	(40)
Other comprehensive income (loss) before reclassifications	0	101	0	46
Amounts reclassified from accumulated other comprehensive loss	1	2	3	6
Net other comprehensive (loss) income	1	103	3	52
AOC Income (Loss), Closing balance	(1)	12	(1)	12
Pension and post-retirement defined benefit plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	(1,856)	(2,800)	(1,915)	(2,878)
Other comprehensive income (loss) before reclassifications	(14)	0	(14)	0
Amounts reclassified from accumulated other comprehensive loss	30	39	89	117
Net other comprehensive (loss) income	16	39	75	117
AOC Income (Loss), Closing balance	(1,840)	(2,761)	(1,840)	(2,761)
Equity Accounted Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOC Income (Loss), Opening balance	102	(10)	(2)	(8)
Other comprehensive income (loss) before reclassifications	37	0	140	(2)
Amounts reclassified from accumulated other comprehensive loss	0	0	1	0
Net other comprehensive (loss) income	37	0	141	(2)
AOC Income (Loss), Closing balance	$ 139	$ (10)	$ 139	$ (10)