Debt - Components of Long-term Debt - C (Narrative) (Detail) - 12 months ended Dec. 31, 2015 - 5.41% Senior Secured Notes [Member] CAD in Millions, $ in Millions	USD ($)	CAD
Debt Instrument [Line Items]
Interest rate		5.41%
Value of locomotive units and other rolling stock used as collateral \| CAD		CAD 130
Final repayment of principal amount \| $	$ 44

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant