Derivative instruments (Summary of Income and Expense Line Items) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	$ 55	$ 114	$ 69	$ 517
Interest expense, net	(302)	(313)	(944)	(988)
Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on fair value hedging relationships, Hedged items	35	(96)	215	(444)
Gains (losses) on fair value hedging relationships, Derivatives designated as hedging instruments	(13)	96	(150)	447
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedges [Member] | Cross-currency swap contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	183	(64)	101	(92)
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	6,104	5,463	17,906	16,323
Product sales [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedges [Member] | Foreign currency contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	$ 41	$ 26	$ 158	$ 62