Derivative instruments (Fair Value of Derivatives) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Assets
Total derivative assets, fair value	$ 351	$ 213
Liabilities
Total derivative liabilities, fair value	487	261
Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	351	213
Liabilities
Total derivative liabilities, fair value	486	260
Derivatives designated as hedging instrument [Member] | Foreign currency contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	68	142
Derivatives designated as hedging instrument [Member] | Foreign currency contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	26	7
Derivatives designated as hedging instrument [Member] | Cross currency swap contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	17	0
Derivatives designated as hedging instrument [Member] | Cross currency swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	456	250
Derivatives designated as hedging instrument [Member] | Forward interest rate contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	0
Derivatives designated as hedging instrument [Member] | Forward interest rate contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	4
Derivatives designated as hedging instrument [Member] | Interest rate swap contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	266	71
Derivatives designated as hedging instrument [Member] | Interest rate swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	0	3
Derivatives not designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	0	0
Liabilities
Total derivative liabilities, fair value	1	1
Derivatives not designated as hedging instrument [Member] | Foreign currency contracts [Member] | Other current assets [Member]
Assets
Total derivative assets, fair value	0	0
Derivatives not designated as hedging instrument [Member] | Foreign currency contracts [Member] | Accrued liabilities [Member]
Liabilities
Total derivative liabilities, fair value	$ 1	$ 1