Business acquisitions - Narrative (Details) $ / shares in Units, shares in Millions											1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 14, 2021 CAD ($) shares	Dec. 14, 2021 USD ($) $ / shares shares	Dec. 02, 2021 CAD ($)	Dec. 02, 2021 USD ($)	Nov. 24, 2021 CAD ($)	Sep. 15, 2021 CAD ($)	Sep. 15, 2021 USD ($)	May 21, 2021 CAD ($)	May 21, 2021 USD ($)	Dec. 22, 2020 CAD ($) mi	Dec. 31, 2021 CAD ($)	Dec. 31, 2022 CAD ($)	Dec. 31, 2022 CAD ($)	Dec. 31, 2021 CAD ($)	Dec. 31, 2020 CAD ($)	Aug. 10, 2021 USD ($)	Mar. 21, 2021 mi
Business Acquisition [Line Items]
Merger termination fee													$ 0	$ (845,000,000)	$ 0
Amount remitted													0	12,299,000,000	0
Shares issued for Kansas City Southern acquisition													(2,000,000)	23,456,000,000
Proceeds from issuance of long-term debt			$ 8,600,000,000	$ 6,700,000,000	$ 2,200,000,000							$ 10,700,000,000
Investment											$ 42,309,000,000	45,091,000,000	45,091,000,000	42,309,000,000
Equity (earnings) loss of Kansas City Southern													(1,074,000,000)	141,000,000	0
Amortization of basis difference													(163,000,000)
Acquisition-related costs													0	247,000,000	0
Financing fees													0	51,000,000	0
Cash, net of cash acquired													0	0	398,000,000
Goodwill											328,000,000	344,000,000	344,000,000	328,000,000	329,000,000
Share capital
Business Acquisition [Line Items]
Shares issued for Kansas City Southern acquisition														23,461,000,000
DRTP
Business Acquisition [Line Items]
Ownership percentage										100.00%
Kansas City Southern
Business Acquisition [Line Items]
Amount remitted						$ 1,773,000,000	$ 1,400,000,000
Investment												$ 45,091,000,000	45,091,000,000
Equity (earnings) loss of Kansas City Southern													(1,074,000,000)
Kansas City Southern
Business Acquisition [Line Items]
Number of route miles acquired | mi																	7,100
Merger termination fee							$ (700,000,000)	$ (845,000,000)	$ (700,000,000)
Enterprise value																$ 31,000,000,000
Assumption of debt																$ 3,800,000,000
Exchange ratio																2.884	2.445
Stock issued (in shares) | shares	262.6	262.6
Shares issued for Kansas City Southern acquisition	$ 23,500,000,000	$ 18,300,000,000
Cash consideration	10,500,000,000	8,200,000,000
Total consideration	$ 36,000,000,000	$ 28,000,000,000
Equity Method Investment, Foreign Currency Translation Adjustment													2,891,000,000
Proceeds from Dividends Received													1,157,000,000
Interest Rate Hedge, Unwinding													212,000,000
Acquisition-related costs														599,000,000
Percentage ownership acquired	100.00%	100.00%
Kansas City Southern | Share capital
Business Acquisition [Line Items]
Consideration transferred, per share (in CAD or USD per share) | $ / shares		$ 90
Kansas City Southern | Preferred stock
Business Acquisition [Line Items]
Consideration transferred, per share (in CAD or USD per share) | $ / shares		$ 37.50
Kansas City Southern | Purchased services and other
Business Acquisition [Line Items]
Acquisition-related costs													74,000,000	183,000,000
Kansas City Southern | Other expense (income)
Business Acquisition [Line Items]
Acquisition-related costs														$ 247,000,000
Kansas City Southern | Equity loss of Kansas City Southern
Business Acquisition [Line Items]
Acquisition-related costs											$ 169,000,000		$ 49,000,000
DRTP
Business Acquisition [Line Items]
Investment										$ 13,000,000
Percentage ownership acquired										83.50%
Cash, net of cash acquired										$ 398,000,000
Reduction of operating costs related to movements through the DRTP															$ (34,000,000)
Miles of rail tunnel acquired | mi										1.6
Previously held equity interest, Percentage										16.50%
Gain on remeasurement of DRTP equity interest										$ 68,000,000
Fair value of previously held equity method investment										81,000,000
Goodwill										90,000,000
Acquired cash and equivalents										$ 6,000,000