Derivative instruments (Locations and Effective Portions of Gain (Loss) Reclassified out of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments Gain Loss [Line Items]
Product sales	$ 5,343	$ 5,199
Interest and other income, net	231	195
Income before income taxes	2,619	2,460
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative Instruments Gain Loss [Line Items]
Income before income taxes	130	131
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge [Member]
Derivative Instruments Gain Loss [Line Items]
Income before income taxes	130	131
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge [Member] | Foreign currency contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Product sales	(34)	57
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge [Member] | Cross-currency swap contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Interest and other income, net	$ 164	$ 74