Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended			47 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011
Stockholders' Equity Note [Abstract]
Shares repurchased	652,016	1,667,592	0	12,082,808
Average purchase price per share	$ 46.99	$ 28.77	$ 0	$ 37.77
Amount spent on repurchased shares	$ 31	$ 48	$ 0	$ 456