Derivative instruments (Locations and Effective Portions of Gain (Loss) Reclassified 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
Derivative Instruments Gain Loss [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
Accumulated net gain (loss) from designated or qualifying cash flow hedges [Member] | Reclassification out of AOCI [Member]
Derivative Instruments Gain Loss [Line Items]
Income before income taxes									638	(139)	143
Accumulated net gain (loss) from designated or qualifying cash flow hedges [Member] | Reclassification out of AOCI [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative Instruments Gain Loss [Line Items]
Income before income taxes									638	(139)	143
Accumulated net gain (loss) from designated or qualifying cash flow hedges [Member] | Reclassification out of AOCI [Member] | Derivatives in cash flow hedging relationships [Member] | Foreign currency contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Product sales									65	308	326
Accumulated net gain (loss) from designated or qualifying cash flow hedges [Member] | Reclassification out of AOCI [Member] | Derivatives in cash flow hedging relationships [Member] | Cross-currency swap contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Interest and other income, net									574	(446)	(182)
Accumulated net gain (loss) from designated or qualifying cash flow hedges [Member] | Reclassification out of AOCI [Member] | Derivatives in cash flow hedging relationships [Member] | Forward interest rate contract [Member]
Derivative Instruments Gain Loss [Line Items]
Interest expense, net									$ (1)	$ (1)	$ (1)