Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income (Numerator):
Net income for basic and diluted EPS	$ 1,825	$ 1,992
Shares (Denominator):
Weighted-average shares for basic EPS (in shares)	590	622
Effect of dilutive securities (in shares)	4	4
Weighted-average shares for diluted EPS (in shares)	594	626
Basic EPS (in usd per share)	$ 3.09	$ 3.20
Diluted EPS (in usd per share)	$ 3.07	$ 3.18