Consolidated Balance Sheet (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Trade, allowance for doubtful accounts	$ 8	$ 11
Preferred stock, shares authorized	50,000,000	50,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	450,000,000	450,000,000
Common stock, outstanding	147,319,438	144,126,032
Treasury stock, shares	645,734	379,631
Series A Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares outstanding	2,500,000	2,500,000
Series B Preferred stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares outstanding	5,221,199	5,311,298