Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value Measurements [Abstract]
Gain (loss) recognized related to valuation adjustments for counterparty default risk	$ (2)	$ 1	$ (1)
Valuation adjustments related to net derivative contracts	$ 1	$ 2