Income taxes (Details) - CAD ($) $ in Millions		3 Months Ended		6 Months Ended
	Apr. 13, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Apr. 14, 2023
Business Acquisition [Line Items]
Effective tax rate		120.88%	24.21%	139.47%	19.59%
Effective tax rate, excluding discrete items		25.18%	24.25%	24.88%	24.25%
Deferred tax (recovery) expense (Note 4)		$ (7,953)	$ 114	$ (7,928)	$ 113
Remeasurement loss of Kansas City Southern (Note 8)		7,175	0	7,175	0
Acquisition-related costs		9		12
Re-evaluation of deferred income tax		51		51
Equity earnings of Kansas City Southern		(26)	(208)	(230)	(406)
Outside basis deferred tax recovery			49	23	17
Value added tax receivable		64		64		$ 80
KCS
Business Acquisition [Line Items]
Deferred tax (recovery) expense (Note 4)	$ (7,832)			7,832
Remeasurement loss of Kansas City Southern (Note 8)	$ 7,175
Acquisition-related costs		119	$ 19	134	$ 39
Amortization of fair value adjustments		$ 75		$ 75