Derivative instruments (Locations and Effective Portions of Gain (Loss) Reclassified out of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	$ 185	$ 231
Income before income taxes	2,314	2,619
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	5,286	5,343
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	(28)	130
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign currency contracts [Member] | Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	14
Accumulated net gain (loss) from cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cross-currency swap contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	(42)
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	(28)	130
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] | Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	14	(34)
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	$ (42)	$ 164