Fair Value Measurements (Details 2) (Level 3, USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 2	$ 3
Issuance of guarantees	1	1
Expiration of guarantees	(1)	(2)
Balance at end of period	$ 2	$ 2