CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	CAD 319	CAD 323	CAD 390	CAD 320	CAD 451	CAD 400	CAD 371	CAD 254	CAD 1,352	CAD 1,476	CAD 875
Net (loss) gain in foreign currency translation adjustments, net of hedging activities									(86)	(32)	3
Change in derivatives designated as cash flow hedges									(69)	(49)	(1)
Change in pension and post-retirement defined benefit plans									1,059	(941)	1,681
Other comprehensive (loss) income before income taxes									904	(1,022)	1,683
Income tax (expense) recovery on above items									(162)	306	(418)
Other comprehensive (loss) income									742	(716)	1,265
Comprehensive income									CAD 2,094	CAD 760	CAD 2,140