Derivative instruments (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets
Total derivative assets, fair value	$ 310	$ 438
Liabilities
Total derivative liabilities, fair value	111	42
Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	306	434
Liabilities
Total derivative liabilities, fair value	107	38
Derivatives designated as hedging instrument [Member] | Cross currency swap contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	22	32
Derivatives designated as hedging instrument [Member] | Cross currency swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	80	12
Derivatives designated as hedging instrument [Member] | Foreign currency contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	234	356
Derivatives designated as hedging instrument [Member] | Foreign currency contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	3	0
Derivatives designated as hedging instrument [Member] | Interest rate swap contracts [Member] | Other current assets/Other noncurrent assets [Member]
Assets
Total derivative assets, fair value	50	46
Derivatives designated as hedging instrument [Member] | Interest rate swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member]
Liabilities
Total derivative liabilities, fair value	24	26
Derivatives not designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	4	4
Liabilities
Total derivative liabilities, fair value	4	4
Derivatives not designated as hedging instrument [Member] | Foreign currency contracts [Member] | Other current assets [Member]
Assets
Total derivative assets, fair value	4	4
Derivatives not designated as hedging instrument [Member] | Foreign currency contracts [Member] | Accrued liabilities [Member]
Liabilities
Total derivative liabilities, fair value	$ 4	$ 4