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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic EPS:
Net income	$ 1,380	$ 1,305	$ 2,554	$ 2,522
Income allocated to RSUs	(7)	(9)	(13)	(17)
Income allocated to common stock for basic EPS	$ 1,373	$ 1,296	$ 2,541	$ 2,505
Weighted average number of shares outstanding, basic (in shares)	916	937	923	938
Basic (in dollars per share)	$ 1.50	$ 1.38	$ 2.75	$ 2.67
Dilutive effect of stock compensation plans (in shares)	11	16	12	16
Diluted EPS:
Net income	$ 1,380	$ 1,305	$ 2,554	$ 2,522
Income allocated to RSUs	(7)	(8)	(13)	(16)
Income allocated to common stock for diluted EPS	$ 1,373	$ 1,297	$ 2,541	$ 2,506
Weighted average number of shares outstanding, diluted (in shares)	927	953	935	954
Diluted (in dollars per share)	$ 1.48	$ 1.36	$ 2.72	$ 2.63