Derivative instruments (Details 3) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets
Total derivative assets, fair value	$ 282	$ 349
Liabilities
Total derivative liabilities, fair value	170	103
Interest rate swap contracts [Member] | Other current assets/other non-current assets [Member] | Derivatives Designated as Hedging Instrument [Member]
Assets
Total derivative assets, fair value	232	195
Interest rate swap contracts [Member] | Accrued liabilities/other noncurrent liabilities [Member] | Derivatives Designated as Hedging Instrument [Member]
Liabilities
Total derivative liabilities, fair value	0	0
Foreign currency contracts [Member] | Other current assets/other non-current assets [Member] | Derivatives Designated as Hedging Instrument [Member]
Assets
Total derivative assets, fair value	50	154
Foreign currency contracts [Member] | Other current assets [Member] | Derivatives Not Designated as Hedging Instrument [Member]
Assets
Total derivative assets, fair value	0	0
Foreign currency contracts [Member] | Accrued liabilities/other noncurrent liabilities [Member] | Derivatives Designated as Hedging Instrument [Member]
Liabilities
Total derivative liabilities, fair value	170	103
Foreign currency contracts [Member] | Accrued liabilities[ Member] | Derivatives Not Designated as Hedging Instrument [Member]
Liabilities
Total derivative liabilities, fair value	0	0
Derivatives Designated as Hedging Instrument [Member]
Assets
Total derivative assets, fair value	282	349
Liabilities
Total derivative liabilities, fair value	170	103
Derivatives Not Designated as Hedging Instrument [Member]
Assets
Total derivative assets, fair value	0	0
Liabilities
Total derivative liabilities, fair value	$ 0	$ 0