Debt - Components of Long-term Debt - D (Narrative) (Detail) - 7.49% Equipment Trust Certificates [Member] CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2015
Debt Instrument [Line Items]
Interest rate		7.49%	7.49%
Value of locomotive units used as collateral | CAD		CAD 117
Final repayment of principal amount | $	$ 11