Stockholders' Equity - Additional Information (Details) (USD $)	1 Months Ended		3 Months Ended				9 Months Ended		12 Months Ended	1 Months Ended		9 Months Ended	1 Months Ended	3 Months Ended
	Jun. 30, 2013	Oct. 31, 2012	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013 Subsidiary	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Aug. 31, 2013 Series A Preferred Stock	Aug. 02, 2013 Series A Preferred Stock	Sep. 30, 2013 Series B Preferred Stock	Aug. 31, 2013 Accelerated Share Repurchase Program [Member]	Sep. 30, 2013 Accelerated Share Repurchase Program [Member]
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							$ 4,000,000		$ 8,000,000
Payments for preferred stock redemption							474,000,000			474,000,000
Payment Of Preferred Stock Redemption Costs										3,000,000
Preferred Stock, Value, Issued											242,000,000
Preferred stock redemption premium			232,000,000				232,000,000			232,000,000
Shares of preferred stock converted												892,662
Common stock issued during period on conversion of convertible securities												7,541,105
Fair value of conversions												158,000,000
Dividends declared per common share			$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.15	$ 0.15
Stock Repurchase Program, Authorized Amount	1,000,000,000	250,000,000											200,000,000
Stock Repurchase Program, Period in Force	2 years	2 years											0 years 3 months 15 days
Share repurchases payment							88,000,000
Shares repurchased during period							5,075,740
Accelerated Share Repurchases, Settlement (Payment) or Receipt													200,000,000
Accelerated Share Repurchases, Initial Delivery Of Shares													7,302,602
Accelerated Share Repurchases, Percentage Of Value Delivered In Initial Shares													80.00%
Accelerated Share Repurchases, Initial Price Paid Per Share													$ 21.91
Accelerated Share Repurchases, Remaining Percentage Of Value To Be Delivered In Shares													20.00%
Adjustments to additional paid-in capital							6,000,000							40,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount							220,000,000
Number of Subsidiaries in which Noncontrolling Interests were Purchased					3
Payments to Noncontrolling Interests					$ 7,000,000		$ 7,000,000