Shareholders' Equity - Activities Under Shares Repurchase Program (Detail) - CAD CAD / shares in Units, CAD in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Statement of Stockholders' Equity [Abstract]
Number of Common Shares repurchased (shares)	0	2,174,788
Weighted-average price per share (in dollars per share)	CAD 0.00	CAD 225.12
Amount of repurchase	CAD 0	CAD 490

The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

No definition available.

Name:	us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant