Derivative instruments (Summary of Income and Expense Line Items) (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
Interest expense, net	(343)	(338)
Amortization of cumulative amount of fair value hedging adjustments for discontinued hedging relationships	3
Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on fair value hedging relationships, Hedged items	(130)
Gains (losses) on fair value hedging relationships, Derivatives designated as hedging instruments	133
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	(42)
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	5,286	$ 5,343
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	$ 14