Stockholders' equity (Reclassifications out of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net	$ 126	$ 267	$ 519	$ 627
Interest expense, net	(355)	(325)	(1,040)	(972)
Income before income taxes	2,094	2,381	7,360	7,383
Provision for income taxes	(235)	(360)	(894)	(1,140)
Net income	1,859	2,021	6,466	6,243
Product sales [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Product sales	5,510	5,453	16,532	16,226
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cash flow hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(33)	140	(221)	601
Provision for income taxes	7	(49)	47	(213)
Net income	(26)	91	(174)	388
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	(103)	26	(352)	(70)
Provision for income taxes	1	(5)	3	(7)
Net income	(102)	21	(349)	(77)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Foreign currency contract [Member] \| Cash flow hedges [Member] \| Product sales [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Product sales	3		(51)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cross-currency swap contract [Member] \| Cash flow hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net	(36)		(170)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cash flow hedges [Member] \| Cash flow hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(33)	140	(221)	601
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cash flow hedges [Member] \| Foreign currency contract [Member] \| Cash flow hedges [Member] \| Product sales [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Product sales	3	(2)	(51)	88
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cash flow hedges [Member] \| Cross-currency swap contract [Member] \| Cash flow hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest and other income, net	(36)	143	(170)	514
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Cash flow hedges [Member] \| Forward interest rate contracts [Member] \| Cash flow hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	$ 0	$ (1)	$ 0	$ (1)

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