Investment Securities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	$ 47,356		$ 47,356		$ 52,473
Weighted average expected constant prepayment rate			11.00%		8.00%
Agency securities, total fair value	900		$ 900
Debt, at fair value	494		494		$ 595
Principal balance of agency securities collaterizing debt issued by securitization trust	(800)		(800)		(1,000)
Principal amount	488		488		587
Gain (loss) associated with consolidated debt	(2)	$ 7	(8)	$ 16
Fair value of CMO securities and interest-only and principal-only strips	1,200		1,200		1,300
Securitized CMO Securities	1,600		1,600		1,800
CMO and Interest Only, Principal Only Securities, Maximum Loss Exposure			222		238
Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unamortized premium balance	2,100		2,100		2,300
Interest Only And Principal Only Strip [Member]
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gain	(6)	$ 10	5	$ 14
TBA securities Fifteen Year and Thirty Year Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Net long TBA position, at fair value	15,600		15,600		7,400
TBA, net carrying value	$ 46		$ 46		$ 14