Derivative instruments (Fair Value of Derivatives) (Details) - Derivatives designated as hedging instrument [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Total derivative assets, fair value	$ 382	$ 286
Liabilities
Total derivative liabilities, fair value	665	485
Foreign currency contracts [Member] | Other current assets/Other assets [Member]
Assets
Total derivative assets, fair value	121	6
Foreign currency contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	49	204
Cross-currency swap contracts [Member] | Other current assets/Other assets [Member]
Assets
Total derivative assets, fair value	261	270
Cross-currency swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	306	220
Interest rate swap contracts [Member] | Other current assets/Other assets [Member]
Assets
Total derivative assets, fair value	0	10
Interest rate swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	$ 310	$ 61