Shareholders' equity - Summary of Information Related to Common Share Balances (Details) - shares shares in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share capital, January 1 (in shares)	930.5	929.7	666.3
Shares issued under stock option plan (in shares)	1.6	0.8	0.8
Shares issued for KCS acquisition (in shares)	0.0	0.0	262.6
Share capital, December 31 (in shares)	932.1	930.5	929.7

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Number of shares of stock issued during the period pursuant to acquisitions.

+ References

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- Definition

Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

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