Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Income (Numerator):
Net income for basic and diluted EPS	$ 2,021	$ 1,803	$ 1,825	$ 1,968	$ 2,179	$ 1,992	$ 5,649	$ 6,139
Shares (Denominator):
Weighted-average shares for basic EPS (in shares)	585			599			588	609
Effect of dilutive securities (in shares)	4			3			4	4
Weighted-average shares for diluted EPS (in shares)	589			602			592	613
Basic EPS (in usd per share)	$ 3.45			$ 3.29			$ 9.61	$ 10.08
Diluted EPS (in usd per share)	$ 3.43			$ 3.27			$ 9.54	$ 10.01