Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss, Net of Tax (Detail) - CAD CAD in Millions	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred losses on settled hedge instruments	CAD (11)	CAD (16)
Unrealized effective losses on cash flow hedges	(89)	(34)
Amounts for defined benefit pension and other post-retirement plans not recognized in income	(1,504)	(2,282)
Equity accounted investments	(2)	(2)
Accumulated other comprehensive loss	(1,477)	(2,219)
Net Investment in U.S. Subsidiaries [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized foreign exchange gain (loss)	870	199
Long-term Debt Designated as Hedge of Net Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized foreign exchange gain (loss)	CAD (741)	CAD (84)