CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 2,444	$ 2,440	$ 1,951
Net gain (loss) in foreign currency translation adjustments, net of hedging activities	18	37	(60)
Change in derivatives designated as cash flow hedges	9	10	38
Change in pension and post-retirement defined benefit plans	(407)	(661)	(449)
Other comprehensive loss before income taxes	(380)	(614)	(471)
Income tax recovery on above items	88	135	169
Other comprehensive income (loss)	(292)	(479)	(302)
Comprehensive income	$ 2,152	$ 1,961	$ 1,649