Derivative instruments (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Total derivative assets, fair value	$ 150	$ 111
Liabilities
Total derivative liabilities, fair value	176	65
Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	150	110
Liabilities
Total derivative liabilities, fair value	176	64
Derivatives not designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	0	1
Liabilities
Total derivative liabilities, fair value	0	1
Cross currency swap contracts [Member] | Other current assets/Other noncurrent assets [Member] | Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	31	65
Cross currency swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member] | Derivatives designated as hedging instrument [Member]
Liabilities
Total derivative liabilities, fair value	64	6
Foreign currency contracts [Member] | Other current assets/Other noncurrent assets [Member] | Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	109	45
Foreign currency contracts [Member] | Other current assets [Member] | Derivatives not designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	0	1
Foreign currency contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member] | Derivatives designated as hedging instrument [Member]
Liabilities
Total derivative liabilities, fair value	11	58
Foreign currency contracts [Member] | Accrued liabilities [Member] | Derivatives not designated as hedging instrument [Member]
Liabilities
Total derivative liabilities, fair value	0	1
Interest rate swap contracts [Member] | Other current assets/Other noncurrent assets [Member] | Derivatives designated as hedging instrument [Member]
Assets
Total derivative assets, fair value	10
Interest rate swap contracts [Member] | Accrued liabilities/Other noncurrent liabilities [Member] | Derivatives designated as hedging instrument [Member]
Liabilities
Total derivative liabilities, fair value	$ 101