Debt (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Debt
Outstanding letters of credit	$ 34	$ 33

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant