Summary of Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) (CAD) In Millions, unless otherwise specified	1 Months Ended
	Feb. 26, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Risk adjusted discount rate	10.00%
Inflation rate	2.00%
Property, plant and equipment		2,949	2,434	1,948
Asset retirement obligations		(287)	(284)	(267)
Other		(109)	(49)	(30)
Net deferred income tax liabilities		2,512	1,397	850
Celtic
Business Acquisition [Line Items]
Property, plant and equipment	414
Total deferred income tax liabilities	414
Asset retirement obligations	(17)
Other	(20)
Total deferred income tax assets	(37)
Net deferred income tax liabilities	377