Profit per share - Computations of Profit Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Profit for the period (A) (in millions of dollars)	[1]	$ 10,792	$ 10,335	$ 6,705
Determination of shares (in millions):
Weighted-average number of common shares outstanding (B) (in shares)		486.7	510.6	526.9
Shares issuable on exercise of stock awards, net of shares assumed to be purchased out of proceeds at average market price (in shares)		2.7	3.0	3.5
Average common shares outstanding for fully diluted computation (C) (in shares)	[2]	489.4	513.6	530.4
Assuming no dilution (A/B) (in dollars per share)		$ 22.17	$ 20.24	$ 12.72
Assuming full dilution (A/C) (in dollars per share)	[2]	$ 22.05	$ 20.12	$ 12.64
Shares outstanding as of December 31 (in shares)		477.9	499.4	516.3

[1] Profit attributable to common shareholders.

[2] Diluted by assumed exercise of stock-based compensation awards using the treasury stock method.