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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic EPS:
Net income	$ 1,947	$ 1,353	$ 5,631	$ 3,907
Income allocated to RSUs	(9)	(6)	(23)	(19)
Income allocated to common stock	$ 1,938	$ 1,347	$ 5,608	$ 3,888
Weighted average number of shares outstanding, basic (in shares)	923	917	923	921
Basic (in dollars per share)	$ 2.10	$ 1.47	$ 6.08	$ 4.22
Dilutive effect of stock compensation plans (in shares)	13	12	13	12
Diluted EPS:
Net income	$ 1,947	$ 1,353	$ 5,631	$ 3,907
Income allocated to RSUs	(9)	(6)	(24)	(19)
Income allocated to common stock for diluted EPS	$ 1,938	$ 1,347	$ 5,607	$ 3,888
Weighted average number of shares outstanding, diluted (in shares)	936	929	936	933
Diluted (in dollars per share)	$ 2.07	$ 1.45	$ 5.99	$ 4.17