Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at January 1	$ (1,517)	$ (1,815)	$ (1,897)
Current period change excluding amounts reclassified from accumulated other comprehensive income	(505)	158	(54)
Amounts reclassified from accumulated other comprehensive income	111	140	136
Balance at December 31	$ (1,911)	$ (1,517)	$ (1,815)