Debt - Components of Long-term Debt - H (Narrative) (Detail) - 4.28% Senior Secured Notes [Member] CAD in Millions, $ in Millions	3 Months Ended
Sep. 30, 2015 CAD	Sep. 30, 2015 USD ($)	Dec. 31, 2015	Sep. 30, 2015 USD ($)	Dec. 31, 2014
Debt Instrument [Line Items]
Interest rate	4.28%		4.28%	4.28%	4.28%
Debt extinguished	CAD 101	$ 76
Final repayment of principal amount	87	66
Early redemption premium	12	$ 9
Accrued interest	CAD 2			$ 1

Amount of interest payable on debt, including, but not limited to, trade payables.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Subparagraph a
-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Subparagraph 5
-Article 9

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant