Income taxes - Deferred Income Tax Assets and Liabilities (Details) $ in Millions, $ in Billions	Dec. 31, 2021 CAD ($)	Dec. 14, 2021 CAD ($)	Dec. 14, 2021 USD ($)	Dec. 31, 2020 CAD ($)
Deferred income tax assets
Amount related to tax losses carried forward	$ 17			$ 17
Liabilities carrying value in excess of tax basis	124			131
Unrealized foreign exchange losses	0			4
Environmental remediation costs	22			22
Other	7			4
Total net deferred income tax assets	170			178
Deferred income tax liabilities
Investment in Kansas City Southern	7,079	$ 7,200	$ 5.6	0
Properties carrying value in excess of tax basis	3,887			3,708
Pensions carrying value in excess of tax basis	441			43
Unrealized foreign exchange gains	13			0
Other	102			93
Total deferred income tax liabilities	11,522			3,844
Total net deferred income tax liabilities	$ 11,352			$ 3,666