Stockholders' equity (Reclassifications out of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product sales	$ 5,569	$ 5,453	$ 5,574	$ 5,199	$ 5,663	$ 5,516	$ 5,474	$ 5,239	$ 21,795	$ 21,892	$ 20,944
Interest and other income, net									928	629	603
Interest expense, net									(1,304)	(1,260)	(1,095)
Income before income taxes									9,597	9,163	7,978
Provision for income taxes									(7,618)	(1,441)	(1,039)
Net income	$ (4,264)	$ 2,021	$ 2,151	$ 2,071	$ 1,935	$ 2,017	$ 1,870	$ 1,900	1,979	7,722	6,939
Reclassification out of AOCI [Member] | Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes									638	(139)	143
Provision for income taxes									(226)	46	(53)
Net income									412	(93)	90
Reclassification out of AOCI [Member] | Available-for-sale securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net									(41)	(61)	(76)
Provision for income taxes									(8)	11	18
Net income									(49)	(50)	(58)
Cash flow hedge [Member] | Reclassification out of AOCI [Member] | Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes									638	(139)	143
Foreign currency contracts [Member] | Cash flow hedge [Member] | Reclassification out of AOCI [Member] | Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product sales									65	308	326
Cross-currency swap contracts [Member] | Cash flow hedge [Member] | Reclassification out of AOCI [Member] | Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net									574	(446)	(182)
Forward interest rate contract [Member] | Cash flow hedge [Member] | Reclassification out of AOCI [Member] | Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net									$ (1)	$ (1)	$ (1)