Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD CAD / shares in Units, CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Stockholders' Equity [Abstract]
Stock Repurchased and Retired During Period, Shares	1,782,200	7,738,489	6,910,000	12,972,177
Weighted-average price per share (in dollars per share)	CAD 192.10	CAD 200.84	CAD 175.08	CAD 203.08
Payments for Repurchase of Common Stock	CAD 342	CAD 1,555	CAD 1,210	CAD 2,635