Investment Securities (Available-for-sale Securities, Unrealized Losses) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) security	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) security	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Purchase of investment securities available-for-sale			$ 724,000,000
Sales of available-for-sale securities			4,558,000,000
Gain on available-for-sale securities		$ 1,000,000		$ 1,000,000
US Government-sponsored Enterprises Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Purchase of investment securities available-for-sale	$ 72,000,000	464,000,000	724,000,000	669,000,000
Agency
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value	$ 13,000,000		$ 13,000,000		$ 53,000,000
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Securities | security	3		3		6
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Unrealized Loss	$ (1,000,000)		$ (1,000,000)		$ 0
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value	$ 244,000,000		$ 244,000,000		$ 305,000,000
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Securities | security	16		16		21
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss	$ (2,000,000)		$ (2,000,000)		$ (2,000,000)
Agency-collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value	$ 0		$ 0		$ 98,000,000
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Securities | security	0		0		10
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Unrealized Loss	$ 0		$ 0		$ (1,000,000)
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value	$ 460,000,000		$ 460,000,000		$ 38,000,000
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Securities | security	35		35		4
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss	$ (4,000,000)		$ (4,000,000)		$ 0
U.S. government sponsored agencies
Schedule of Available-for-sale Securities [Line Items]
Sales of available-for-sale securities	$ 0	$ 40,000,000	$ 0	$ 58,000,000