Stockholders' Equity - Additional Information (Details)				1 Months Ended	3 Months Ended					9 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($) shares	Jul. 02, 2014 $ / shares	Jan. 31, 2008 shares	Aug. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 $ / shares	Jun. 30, 2015 $ / shares	Mar. 31, 2015 $ / shares	Mar. 31, 2013 USD ($) Subsidiary	Sep. 29, 2014 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Jul. 30, 2014 USD ($)	Aug. 02, 2013 USD ($)
Class of Stock [Line Items]
Preferred stock, shares authorized | shares					50,000,000						50,000,000	50,000,000
Preferred stock, par value | $ / shares					$ 0.01						$ 0.01	$ 0.01
Preferred shares outstanding | shares					0						0	0
Payment for preferred stock redemption													$ 474,000,000
Preferred stock carrying value					$ 0						$ 0	$ 0
Preferred stock redemption premium													$ 232,000,000
Terms of conversion - closing price of common stock | $ / shares		$ 22.24
Terms of conversion - consecutive trading days		20 days
Common stock conversion price of preferred shares | $ / shares		$ 11.93
Conversion Notice Period		90 days
Common stock, shares authorized | shares					450,000,000						450,000,000	450,000,000
Common stock, par value | $ / shares					$ 0.01						$ 0.01	$ 0.01
Common stock, shares issued | shares					150,092,003						150,092,003
Common stock, shares outstanding | shares					150,068,040						150,068,040	166,070,057
Treasury stock, shares | shares					23,963						23,963	1,588,990
Quarterly dividend declared | $ / shares					$ 0.06	$ 0.06	$ 0.06	$ 0.05			$ 0.23	$ 0.20	$ 0.20
Aggregated dividends declared											$ 37,000,000	$ 32,000,000	$ 30,000,000
Aggregate dividends paid											$ 37,000,000	$ 32,000,000	30,000,000
Treasury stock reissued | shares												14,879,935
Treasury stock reissued, charge to additional paid-in capital												$ 127,000,000
Treasury shares retired | shares											18,100,000	14,600,000
Treasury stock retired, charge to additional paid-in capital											$ 0	$ 0
Share repurchase program amount														$ 1,400,000,000
Cash spent to repurchase common stock											$ 311,000,000	$ 260,000,000	$ 337,000,000
Shares repurchased | shares											16,412,485
Number of subsidiaries in which noncontrolling interests were purchased | Subsidiary									3
Payments to Noncontrolling Interests									$ 7,000,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares issued | shares			2,500,000.0
Preferred stock dividend rate percentage			4.00%
Payment for preferred stock redemption				$ 474,000,000
Payment of preferred stock redemption costs				3,000,000
Preferred stock carrying value															$ 242,000,000
Preferred stock redemption premium				$ 232,000,000
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares issued | shares			5,400,000.0
Preferred stock dividend rate percentage			4.00%
Shares of preferred stock converted | shares	1,506,972									2,296,802		1,772,693	1,417,425
Common shares issued upon conversion | shares	12,631,780									19,517,593			11,985,254
Total fair value of the conversions	$ 250,000,000									$ 409,000,000			$ 249,000,000
Additional Paid-in Capital [Member]
Class of Stock [Line Items]
Treasury stock retired, charge to additional paid-in capital											$ 346,000,000	$ 294,000,000