Variable interest entities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 CAD ($)
Variable Interest Entity [Line Items]
Future minimum lease payments before tax	$ 311
Kansas City Southern
Variable Interest Entity [Line Items]
Ownership percentage	100.00%
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Lease payments after tax	$ 14
Future minimum lease payments before tax	$ 107
Period over which lease payments will be paid	9 years