Stockholders' Equity - Additional Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Common stock, shares authorized	1,125,000,000.000	0
Common stock, par value	$ 0.20	$ 0
Common stock shares outstanding (in shares)	423,000,000
Common shares unissued but encumbered (in shares)	60,000,000
Common stock dividends	$ 0	$ 0	$ 0
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock shares outstanding (in shares)	3,300,000	0
Preferred stock dividend rate	6.97%
Preferred stock dividend rate (usd per share)	$ 3.485
Preferred stock liquidation preference (usd per share)	$ 50
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock shares outstanding (in shares)	4,000,000	0
Preferred stock, dividend payment terms	3-month LIBOR plus 170 basis points per annum
Preferred stock liquidation preference (usd per share)	$ 100
Three Month LIBOR [Member] | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividend rate	1.70%