Stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			$ 16,903				$ 16,903
Net income	$ 1,364			$ 1,362			3,838	$ 3,594
Other comprehensive income (loss), net of taxes	7			$ 5			(9)	10
Balance, ending	$ 16,627						16,627
Cash dividends declared per common share (in dollars per share)	$ 1.36	$ 1.36	$ 1.36	$ 1.30	$ 1.30	$ 1.30
Cash dividends paid per common share (in dollars per share)	$ 1.36	$ 1.36	$ 1.36	$ 1.30	$ 1.30	$ 1.30
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning	$ 1,741	$ 1,741	$ 1,741	$ 1,741	$ 1,741	$ 1,741	1,741	1,741
Balance, ending	1,741	1,741	1,741	1,741	1,741	1,741	1,741	1,741
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning	4,245	4,058	3,935	3,666	3,439	3,362	3,935	3,362
Common stock issued for stock-based awards	72	59	8	62	111	(29)
Stock compensation	93	129	116	87	116	106
Other		(1)	(1)	(2)
Balance, ending	4,410	4,245	4,058	3,813	3,666	3,439	4,410	3,813
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning	52,249	52,196	52,262	52,135	52,199	52,283	52,262	52,283
Net income	1,364	1,295	1,179	1,362	1,127	1,105
Dividends declared and paid	(1,236)	(1,235)	(1,238)	(1,187)	(1,185)	(1,183)
Dividend equivalents on RSUs	(7)	(7)	(7)	(6)	(6)	(7)
Other	(1)					1
Balance, ending	52,369	52,249	52,196	52,304	52,135	52,199	52,369	52,304
Treasury Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning	(41,676)	(41,442)	(40,895)	(40,128)	(40,193)	(40,284)	(40,895)	(40,284)
Common stock issued for stock-based awards	53	56	110	55	137	94
Stock repurchases	(121)	(290)	(657)	(322)	(72)	(3)
Balance, ending	(41,744)	(41,676)	(41,442)	(40,395)	(40,128)	(40,193)	(41,744)	(40,395)
AOCI
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning	(156)	(147)	(140)	(200)	(203)	(205)	(140)	(205)
Other comprehensive income (loss), net of taxes	7	(9)	(7)	5	3	2
Balance, ending	$ (149)	$ (156)	$ (147)	$ (195)	$ (200)	$ (203)	$ (149)	$ (195)