Derivative instruments (Summary of Income and Expense Line Items) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	$ 114	$ 126	$ 517	$ 519
Interest expense, net	(313)	(355)	(988)	(1,040)
Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on fair value hedging relationships, Hedged items	(96)	48	(444)	278
Gains (losses) on fair value hedging relationships, Derivatives designated as hedging instruments	96	(44)	447	(259)
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	(64)	(36)	(92)	(170)
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	5,463	5,510	16,323	16,532
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	$ 26	$ 3	$ 62	$ (51)

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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