Stockholders' Equity - Schedule of Preferred Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Preferred stock carrying value including APIC	$ 1,822	$ 853
Depository share interest in preferred stock	0.025
Series B Preferred Stock
Class of Stock [Line Items]
Non-cumulative Fixed Dividend Rate per Annum (as percent)	6.00%	6.00%	6.00%
Redemption Price per Depositary Share (in dollars per share)	$ 25
Number of Depositary Shares (in shares)	35,000,000
Preferred stock carrying value including APIC	853	853
Series C Preferred Stock
Class of Stock [Line Items]
Non-cumulative Fixed Dividend Rate per Annum (as percent)	6.25%
Redemption Price per Depositary Share (in dollars per share)	$ 25
Number of Depositary Shares (in shares)	20,000,000
Preferred stock carrying value including APIC	484
Series D Preferred Stock
Class of Stock [Line Items]
Non-cumulative Fixed Dividend Rate per Annum (as percent)	6.70%
Redemption Price per Depositary Share (in dollars per share)	$ 25
Number of Depositary Shares (in shares)	20,000,000
Preferred stock carrying value including APIC	$ 485