Stock-based compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount by which the pool of available shares will be reduced for each stock option granted (in shares)		1
The amount of common stock available under the plan for future grants and/or issuances (in shares)		59,000,000
Total unrecognized compensation cost related to nonvested awards		$ 510
Weighted average number of years over which compensation cost related to nonvested awards is expected to be recognized (in years)		1 year 9 months 18 days
Period over which the grants of equity instruments vest (in years)		3 years
Number of common shares issued for each performance unit earned (in shares)		1	1	1
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The number of shares by which the pool of available shares will be reduced for other types of awards granted (in shares)		1.9
Number of shares added back for tax withholding on full value awards (in shares)		1.9
Awards accelerated and settled	$ 42
Weighted average grant date fair value, granted (in usd per share)		$ 301.36	$ 237.70	$ 234.47
Total fair value of units that vested during the year		$ 401	$ 309	$ 192
Units outstanding (in shares)	3,900,000	3,500,000	3,900,000
Weighted-average grant date fair value (in usd per share)	$ 246.43	$ 265.07	$ 246.43
Units granted (in shares)		1,500,000
Units, forfeited (in shares)		300,000
Weighted average grant date fair value, forfeited (in usd per share)		$ 267.28
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of stock options from date of grant (in years)		10 years
Total intrinsic value of stock options exercised during the year		$ 70	$ 33	67
Actual tax benefits realized from tax deductions from option exercises		$ 15	$ 7	$ 14
Performance units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The number of shares by which the pool of available shares will be reduced for other types of awards granted (in shares)		1.9
Number of shares added back for tax withholding on full value awards (in shares)		1.9
Weighted average grant date fair value, granted (in usd per share)		$ 321.61	$ 252.49	$ 247.48
Total fair value of units that vested during the year		$ 182	$ 109	$ 150
Total unrecognized compensation cost related to nonvested awards		$ 87
Weighted average number of years over which compensation cost related to nonvested awards is expected to be recognized (in years)		1 year
Units outstanding (in shares)	1,700,000	1,400,000	1,700,000
Weighted-average grant date fair value (in usd per share)	$ 251.41	$ 263.86	$ 251.41
Units granted (in shares)		300,000
Units, forfeited (in shares)		100,000
Weighted average grant date fair value, forfeited (in usd per share)		$ 261.03