Income Taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Current income tax expense	CAD 233	CAD 373	CAD 208
Origination and reversal of temporary differences	336	105	317
Effect of tax rate increases	0	23	0
Effect of hedge of net investment in foreign subsidiaries	(20)	100	42
Other	4	6	(5)
Total deferred income tax expense	320	234	354
Income tax expense	553	607	562
Income before income tax expense
Canada	1,513	1,099	1,269
Foreign	639	860	769
Income before income tax expense	2,152	1,959	2,038
Current
Canada	165	173	50
Foreign	68	200	158
Total current income tax expense	233	373	208
Deferred
Canada	207	163	292
Foreign	113	71	62
Total deferred income tax expense	320	234	354
Income tax expense	CAD 553	CAD 607	CAD 562