Stockholders' Equity - Schedule of Preferred Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended
	May. 31, 2015	Nov. 30, 2014	Feb. 28, 2014	Aug. 31, 2012	Mar. 31, 2016
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)				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 (shares)			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 (shares)		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 (shares)	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