Schedule II - Valuation and Qualifying Accounts (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accruals for legal, personal injury and casualty-related claims [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance at January 1	$ 118	$ 130	$ 133
Additions charged to expenses	93	66	67
Payments and other reductions	(60)	(77)	(71)
Impact of FX	1	(1)	1
Ending balance at December 31	152	118	130
Environmental liabilities [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance at January 1	78	85	93
Additions charged to expenses	6	5	6
Payments and other reductions	(7)	(8)	(12)
Impact of FX	5	(4)	(2)
Ending balance at December 31	$ 82	$ 78	$ 85