Investment Securities (Components Of Investment Securities) (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 Investments [Line Items]
Agency securities transferred to consolidated VIEs		$ 890		$ 890		$ 1,029
Amortized cost		45,982		45,982		52,147
Total agency MBS, at fair value		47,218		47,218		52,360
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure		$ 47,356		$ 47,356		$ 52,473
Weighted average coupon		3.64%		3.64%		3.63%	[1]
Weighted average yield		2.68%		2.68%		2.78%	[2]
Unamortized Principal Balance Of Interest Only Strips				$ 1,000		$ 1,000
Future Prepayment Rate Assumption Of Investment Portfolio				11.00%		8.00%
Non-Agency Securities Unrealized Gain		$ 2		$ 2		$ 0
Non-Agency Securities Unrealized Loss		0		0		(1)
Mortgage Backed Securities Amortized Cost		46,304		46,304		52,464
Mortgage Backed Securities Unrealized Gain		1,065		1,065		407
Mortgage Backed Securities Unrealized Loss		(13)		(13)		(398)
Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		43,996		43,996		49,955
Unamortized discount		(30)		(30)		(36)
Unamortized premium		2,016		2,016		2,228
Amortized cost		45,982		45,982		52,147
Gross unrealized gains				1,021		368
Gross unrealized losses				(10)		(395)
Total available-for-sale securities, at fair value		46,993		46,993		52,120
Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Securities Remeasured at Fair Value through earnings, Amortized Cost		322		322		317
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				44		39
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				(3)		(3)
Securities Remeasured at Fair Value Through Earnings, Debt Securities		363		363		353
Securities remeasured at fair value through earnings, Par Value		216		216		208
Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		(37)		(37)		(42)
Unamortized premium		143		143		151
Fannie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 36,506		$ 36,506		$ 41,214
Weighted average coupon	[1]	3.63%		3.63%		3.62%
Weighted average yield	[2]	2.68%		2.68%		2.79%
Fannie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		$ 33,919		$ 33,919		$ 39,205
Unamortized discount		(27)		(27)		(32)
Unamortized premium		1,494		1,494		1,707
Amortized cost		35,386		35,386		40,880
Gross unrealized gains				817		286
Gross unrealized losses				(6)		(283)
Total available-for-sale securities, at fair value		36,197		36,197		40,883
Fannie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Securities Remeasured at Fair Value through earnings, Amortized Cost		270		270		298
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				41		35
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				(2)		(2)
Securities Remeasured at Fair Value Through Earnings, Debt Securities		309		309		331
Securities remeasured at fair value through earnings, Par Value		181		181		208
Fannie Mae [Member] | Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		(37)		(37)		(42)
Unamortized premium		126		126		132
Freddie Mac [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 10,662		$ 10,662		$ 11,081
Weighted average coupon	[1]	3.69%		3.69%		3.69%
Weighted average yield	[2]	2.67%		2.67%		2.77%
Freddie Mac [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		$ 9,930		$ 9,930		$ 10,575
Unamortized discount		(3)		(3)		(4)
Unamortized premium		520		520		519
Amortized cost		10,447		10,447		11,090
Gross unrealized gains				201		80
Gross unrealized losses				(4)		(111)
Total available-for-sale securities, at fair value		10,644		10,644		11,059
Freddie Mac [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Securities Remeasured at Fair Value through earnings, Amortized Cost		16		16		19
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				3		4
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				(1)		(1)
Securities Remeasured at Fair Value Through Earnings, Debt Securities		18		18		22
Securities remeasured at fair value through earnings, Par Value		0		0		0
Freddie Mac [Member] | Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		0		0		0
Unamortized premium		16		16		19
Ginnie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 50		$ 50		$ 65
Weighted average coupon	[1]	2.81%		2.81%		3.18%
Weighted average yield	[2]	1.96%		1.96%		1.97%
Ginnie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		$ 48		$ 48		$ 62
Unamortized discount		0		0		0
Unamortized premium		1		1		1
Amortized cost		49		49		63
Gross unrealized gains				1		2
Gross unrealized losses				0		0
Total available-for-sale securities, at fair value		50		50		65
Ginnie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Securities Remeasured at Fair Value through earnings, Amortized Cost		0		0		0
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				0		0
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				0		0
Securities Remeasured at Fair Value Through Earnings, Debt Securities		0		0		0
Securities remeasured at fair value through earnings, Par Value		0		0		0
Ginnie Mae [Member] | Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		0		0		0
Unamortized premium		0		0		0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Investments [Line Items]
Amortized cost		100		100		114
Total Securities		$ 102		$ 102		$ 113
Weighted average coupon	[1]	3.50%		3.50%		3.50%
Weighted average yield	[2]	3.00%		3.00%		3.33%
Trading Securities, Other						$ 113
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		$ 99		$ 99		113
Unamortized discount		0		0		0
Unamortized premium		1		1		1
Amortized cost		100		100		114
Gross unrealized gains				2		0
Gross unrealized losses				0		(1)
Total available-for-sale securities, at fair value		102		102		113
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Securities Remeasured at Fair Value through earnings, Amortized Cost		0		0		0
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				0		0
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				0		0
Securities Remeasured at Fair Value Through Earnings, Debt Securities		0		0		0
Securities remeasured at fair value through earnings, Par Value		0		0		0
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		0		0		0
Unamortized premium		$ 0		$ 0		$ 0
Credit Risk Transfer Securities [Member]
Schedule of Investments [Line Items]
Weighted average coupon		4.91%		4.91%
Weighted average yield		4.85%		4.85%
Trading Securities, Other		$ 36		$ 36
Credit Risk Transfer Securities [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Par value		0		0
Unamortized discount		0		0
Unamortized premium		0		0
Amortized cost		0		0
Gross unrealized gains				0
Gross unrealized losses				0
Total available-for-sale securities, at fair value		0		0
Credit Risk Transfer Securities [Member] | Securities Remeasured at Fair Value [Member]
Schedule of Investments [Line Items]
Unamortized discount		0		0
Unamortized premium		1		1
Securities Remeasured at Fair Value through earnings, Amortized Cost		36		36
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Gain				0
Securities Remeasured at Fair Value Through Earnings, Gross Unrealized Loss				0
Securities Remeasured at Fair Value Through Earnings, Debt Securities		36		36
Securities remeasured at fair value through earnings, Par Value		35		35
Total Securities		36		36
Interest Only And Principal Only Strip [Member]
Schedule of Investments [Line Items]
Unrealized Gain (Loss) on Securities		$ (6)	$ 10	$ 5	$ 14

[1] he underlying unamortized principal balance ("UPB") of interest-only securities of $1.0 billion

[2] Incorporates a weighted average future constant prepayment rate assumption of 11% based on forward rates as of September 30, 2016