Stockholders' Equity - Schedule of Preferred Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Proceeds from issuance of preferred stock	$ 742	$ 1,470	$ 0
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary Shares Issued	20,000,000
Liquidation preference per share (USD per share)	$ 25
Series C Preferred Stock
Class of Stock [Line Items]
Ownership Interest per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock	$ 488
Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary Shares Issued	30,000,000
Liquidation preference per share (USD per share)	$ 25
Series D Preferred Stock
Class of Stock [Line Items]
Ownership Interest per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock	$ 742
Series E Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary Shares Issued	30,000,000
Liquidation preference per share (USD per share)	$ 25
Series E Preferred Stock
Class of Stock [Line Items]
Ownership Interest per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock	$ 728
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary Shares Issued	750,000
Liquidation preference per share (USD per share)	$ 1,000
Series F Preferred Stock
Class of Stock [Line Items]
Ownership Interest per Depositary Share	1.00%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock	$ 742