INTERIM CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (unaudited) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 436	$ 480	$ 784	$ 911
Net (loss) gain in foreign currency translation adjustments, net of hedging activities	(16)	14	(36)	19
Change in derivatives designated as cash flow hedges	14	4	35	9
Change in pension and post-retirement defined benefit plans	29	37	58	75
Other comprehensive (loss) income before income taxes	27	55	57	103
Income tax recovery (expense) on above items	5	(26)	11	(44)
Other comprehensive income (loss)	32	29	68	59
Comprehensive income	$ 468	$ 509	$ 852	$ 970