Derivative instruments (Summary of Income and Expense Line Items) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest and other income, net	$ 11	$ 185
Interest expense, net	(346)	(343)
Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on fair value hedging relationships, Hedged items	210	(130)
Gains (losses) on fair value hedging relationships, Derivatives designated as hedging instruments	(190)	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	(133)	(42)
Product sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Product sales	5,894	5,286
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	$ 49	$ 14

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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