Derivative instruments (Summary of Income and Expense Line Items) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	$ 218	$ 162	$ 403	$ 393
Interest expense, net	(332)	(347)	(675)	(685)
Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on fair value hedging relationships, Hedged items	(218)	58	(348)	230
Gains (losses) on fair value hedging relationships, Derivatives designated as hedging instruments	218	(51)	351	(215)
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	14	(298)	(28)	(134)
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	5,574	5,679	10,860	11,022
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	$ 22	$ (20)	$ 36	$ (54)

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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