Stock-based compensation - Schedule of stock-based compensation activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Shares
Outstanding (in shares)	5,141,363
Granted to officers and key employees (in shares)	296,295
Exercised (in shares)	(1,679,281)
Forfeited/expired (in shares)	(25,515)
Outstanding (in shares)	3,732,862	5,141,363
Exercisable (in shares)	2,608,265
Weighted- Average Exercise Price
Outstanding (in dollars per shares)	$ 169.57
Granted to officers and key employees (in dollars per shares)	338.65
Exercised (in dollars per shares)	141.77
Forfeited / expired (in dollars per shares)	202.08
Outstanding (in dollars per shares)	195.28	$ 169.57
Exercisable at year-end (in dollars per share)	$ 167.72
Weighted-Average Remaining Contractual Life (Years), Outstanding	6 years
Weighted-Average Remaining Contractual Life (Years), Exercisable	5 years 29 days
Aggregate Intrinsic Value, Outstanding	$ 625
Aggregate Intrinsic Value, Exercisable	$ 509
RSUs
Shares
Beginning of year, outstanding (in shares)	829,386
Granted to officers and key employees (in shares)	391,784
Vested (in shares)	(427,095)
Forfeited/expired (in shares)	(17,438)
End of year, outstanding (in shares)	776,637	829,386
Weighted- Average Grant Date Fair Value
Outstanding (in dollars per shares)	$ 226.44
Granted to officers and key employees (in dollars per shares)	338.65	$ 252.24	$ 196.06
Vested (in dollars per shares)	221.56
Forfeited (in dollars per shares)	282.89
Outstanding (in dollars per shares)	$ 284.36	$ 226.44
PRSUs
Shares
Beginning of year, outstanding (in shares)	480,759
Granted to officers and key employees (in shares)	178,236
Vested (in shares)	(259,136)
Forfeited/expired (in shares)	(9,846)
End of year, outstanding (in shares)	390,013	480,759
Weighted- Average Grant Date Fair Value
Outstanding (in dollars per shares)	$ 223.09
Granted to officers and key employees (in dollars per shares)	408.64	$ 251.97	$ 195.17
Vested (in dollars per shares)	196.70
Forfeited (in dollars per shares)	269.79
Outstanding (in dollars per shares)	$ 321.58	$ 223.09

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).