Basis of presentation and significant accounting policies and practices - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Basic EPS:
Net income	$ 1,179	$ 1,105
Income allocated to RSUs	(6)	(5)
Income allocated to common stock	$ 1,173	$ 1,100
Weighted average number of shares outstanding, basic (in shares)	910	910
Basic (in dollars per share)	$ 1.29	$ 1.21
Dilutive effect of stock compensation plans (in shares)	6	7
Diluted EPS:
Net income	$ 1,179	$ 1,105
Income allocated to RSUs	(6)	(5)
Income allocated to common stock for diluted EPS	$ 1,173	$ 1,100
Weighted average number of shares outstanding, diluted (in shares)	916	917
Diluted (in dollars per share)	$ 1.28	$ 1.20