Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Income (Numerator):
Net income for basic and diluted EPS	$ 1,803	$ 1,825	$ 2,179	$ 1,992	$ 3,628	$ 4,171
Shares (Denominator):
Weighted-average shares for basic EPS (in shares)	588		607		589	615
Effect of dilutive securities (in shares)	4		3		4	3
Weighted-average shares for diluted EPS (in shares)	592		610		593	618
Basic EPS (in usd per share)	$ 3.07		$ 3.59		$ 6.16	$ 6.78
Diluted EPS (in usd per share)	$ 3.05		$ 3.57		$ 6.12	$ 6.75