Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income (Numerator):
Net income for basic and diluted EPS	$ 1,870	$ 1,653	$ 3,770	$ 3,276
Shares (Denominator):
Weighted-average shares for basic EPS	751	760	753	761
Effect of dilutive securities	5	8	6	8
Weighted-average shares for diluted EPS	756	768	759	769
Basic EPS (in usd per share)	$ 2.49	$ 2.18	$ 5.01	$ 4.30
Diluted EPS (in usd per share)	$ 2.47	$ 2.15	$ 4.97	$ 4.26