Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income (Numerator):
Net income for basic and diluted EPS	$ 1,653	$ 1,547	$ 3,276	$ 2,620
Shares (Denominator):
Weighted-average shares for basic EPS	760	759	761	758
Effect of dilutive securities	8	9	8	10
Weighted-average shares for diluted EPS	768	768	769	768
Basic EPS (in usd per share)	$ 2.18	$ 2.04	$ 4.30	$ 3.46
Diluted EPS (in usd per share)	$ 2.15	$ 2.01	$ 4.26	$ 3.41