Schedule II - Valuation and Qualifying Accounts (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accruals for personal injury and other claims provision
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance at January 1	$ 141	$ 152	$ 118
Additions charged to expenses	105	142	93
Payments and other reductions	(119)	(152)	(60)
Impact of FX	(1)	(1)	1
Ending balance at December 31	126	141	152
Environmental liabilities
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance at January 1	77	82	78
Additions charged to expenses	10	6	6
Payments and other reductions	(6)	(8)	(7)
Impact of FX	(1)	(3)	5
Ending balance at December 31	$ 80	$ 77	$ 82