Stockholders' Equity - Additional Information (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2013	Oct. 31, 2012	Jun. 30, 2013	Mar. 31, 2013 Subsidiary	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Class of Stock [Line Items]
Preferred dividends description						Dividends on our 4.0% Series A Convertible Preferred Stock and 4.0% Series B Convertible Preferred Stock (preferred stock) are accrued monthly and are payable in cash as approved by the Board of Directors.
Series A and Series B preferred stock dividend rate percentage						4.00%
Preferred dividends accrued						$ 8		$ 8
Dividends declared per common share			$ 0.05	$ 0.05	$ 0.05	$ 0.10	$ 0.10
Stock Repurchase Program, Authorized Amount	1,000	250
Stock Repurchase Program, Period in Force	2 years	2 years
Stock Repurchased During Period Shares One						4,947,677
Stock Repurchase Program, Remaining Authorized Repurchase Amount			899
Number of Subsidiaries in which Noncontrolling Interests were Purchased				3
Payments to Noncontrolling Interests				7		7
Series B Preferred Stock
Class of Stock [Line Items]
Conversion of Stock, Shares Converted			148,608
Stock Issued During Period, Shares, Conversion of Convertible Securities			1,252,546
Shares Subject To Conversion Fair Value Of Conversions			$ 23