Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income (Numerator):
Net income for basic and diluted EPS	$ 2,151	$ 1,870	$ 4,222	$ 3,770
Shares (Denominator):
Weighted-average shares for basic EPS	734	751	736	753
Effect of dilutive securities	4	5	4	6
Weighted-average shares for diluted EPS	738	756	740	759
Basic EPS (in usd per share)	$ 2.93	$ 2.49	$ 5.74	$ 5.01
Diluted EPS (in usd per share)	$ 2.91	$ 2.47	$ 5.71	$ 4.97