Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Loss - Components of Other Comprehensive Income (Loss) and Related Tax Effects (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unrealized foreign exchange (loss) gain on: Before tax amount
Translation of the net investment in U.S. subsidiaries	CAD 671	CAD 287	CAD 220
Translation of the U.S. dollar-denominated long-term debt designated as a hedge of the net investment in U.S. subsidiaries	(757)	(319)	(217)
Change in derivatives designated as cash flow hedges: Before tax amount
Realized gain on cash flow hedges recognized in income	7	(3)	(19)
Unrealized loss on cash flow hedges	(76)	(46)	18
Change in pension and other benefits actuarial gains and losses	1,058	(873)	1,603
Change in prior service pension and other benefit costs	1	(68)	78
Other comprehensive income (loss)	904	(1,022)	1,683
Unrealized foreign exchange (loss) gain on: Income tax recovery (expense)
Translation of the net investment in U.S. subsidiaries	0	0	0
Translation of the U.S. dollar-denominated long-term debt designated as a hedge of the net investment in U.S. subsidiaries	100	42	28
Change in derivatives designated as cash flow hedges: Income tax recovery (expense)
Realized gain on cash flow hedges recognized in income	(2)	0	0
Unrealized loss on cash flow hedges	21	12	0
Change in pension and other benefits actuarial gains and losses	(281)	234	(427)
Change in prior service pension and other benefit costs	0	18	(19)
Other comprehensive income (loss)	(162)	306	(418)
Unrealized foreign exchange (loss) gain on: Net of tax amount
Translation of the net investment in U.S. subsidiaries	671	287	220
Translation of the U.S. dollar-denominated long-term debt designated as a hedge of the net investment in U.S. subsidiaries	(657)	(277)	(189)
Change in derivatives designated as cash flow hedges: Net of tax amount
Realized gain on cash flow hedges recognized in income	5	(3)	(19)
Unrealized loss on cash flow hedges	(55)	(34)	18
Change in pension and other benefits actuarial gains and losses	777	(639)	1,176
Change in prior service pension and other benefit costs	1	(50)	59
Other comprehensive (loss) income	CAD 742	CAD (716)	CAD 1,265