Stockholders' equity (Reclassifications out of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Product sales	$ 5,574	$ 5,474	$ 10,773	$ 10,713
Interest and other income, net	165	137	360	287
Total before income tax	2,542	2,204	5,002	4,462
Tax expense	(391)	(334)	(780)	(692)
Net of taxes	2,151	1,870	4,222	3,770
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Product sales	33	79	90	175
Interest and other income, net	297	(212)	371	(142)
Total before income tax	330	(133)	461	33
Tax expense	(117)	49	(164)	(12)
Net of taxes	213	(84)	297	21
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale Securities [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net	(47)	(23)	(96)	(53)
Tax expense	(2)	8	(2)	8
Net of taxes	$ (49)	$ (15)	$ (98)	$ (45)