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, 2022	Mar. 31, 2021
Basic EPS:
Net income	$ 2,201	$ 1,753
Income allocated to RSUs	(9)	(8)
Income allocated to common stock	$ 2,192	$ 1,745
Weighted average number of shares outstanding, basic (in shares)	923	922
Basic (in dollars per share)	$ 2.37	$ 1.89
Dilutive effect of stock compensation plans (in shares)	11	13
Diluted EPS:
Net income	$ 2,201	$ 1,753
Income allocated to RSUs	(9)	(8)
Income allocated to common stock for diluted EPS	$ 2,192	$ 1,745
Weighted average number of shares outstanding, diluted (in shares)	934	935
Diluted (in dollars per share)	$ 2.35	$ 1.87