Consolidated Balance Sheet (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Trade, allowance for doubtful accounts	$ 8	$ 8
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	145,695,504	148,264,067
Treasury stock, shares	6,966,217	1,797,988
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	5,072,591	5,221,199