Investment Securities (Components Of Investment Securities) (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Amortized cost		$ 53,899	$ 55,776
Total agency MBS, at fair value		$ 54,817	$ 56,748
Weighted average coupon		3.61%	3.65%	[1]
Weighted average yield		2.76%	2.74%	[2]
Unamortized Principal Balance Of Interest Only Strips		$ 1,000	$ 1,200
Weighted Average Contractual Interest Rate Of Interest Only Strips		5.42%	5.46%
Unamortized Principal Balance Of Principal Only Strips		$ 216	$ 242
Future Prepayment Rate Assumption Of Investment Portfolio		9.00%	9.00%
Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Agency MBS, par		$ 51,687	$ 53,422
Unamortized discount		(37)	(42)
Unamortized premium		2,249	2,396
Amortized cost		53,899	55,776
Gross unrealized gains		700	758
Gross unrealized losses		(145)	(188)
Total available-for-sale agency MBS, at fair value		54,454	56,346
Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		317	372
Gross unrealized gains		48	33
Gross unrealized losses		(2)	(3)
Total agency MBS measured at fair value through earnings		363	402
Fannie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 42,378	$ 45,451
Weighted average coupon	[1]	3.60%	3.63%
Weighted average yield	[2]	2.76%	2.75%
Fannie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Agency MBS, par		$ 39,898	$ 42,749
Unamortized discount		(33)	(37)
Unamortized premium		1,718	1,880
Amortized cost		41,583	44,592
Gross unrealized gains		555	610
Gross unrealized losses		(99)	(127)
Total available-for-sale agency MBS, at fair value		42,039	45,075
Fannie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		297	348
Gross unrealized gains		43	30
Gross unrealized losses		(1)	(2)
Total agency MBS measured at fair value through earnings		339	376
Freddie Mac [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 11,866	$ 11,185
Weighted average coupon	[1]	3.67%	3.70%
Weighted average yield	[2]	2.77%	2.73%
Freddie Mac [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Agency MBS, par		$ 11,230	$ 10,566
Unamortized discount		(4)	(5)
Unamortized premium		523	514
Amortized cost		11,749	11,075
Gross unrealized gains		139	145
Gross unrealized losses		(46)	(61)
Total available-for-sale agency MBS, at fair value		11,842	11,159
Freddie Mac [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		20	24
Gross unrealized gains		5	3
Gross unrealized losses		(1)	(1)
Total agency MBS measured at fair value through earnings		24	26
Ginnie Mae [Member]
Schedule of Investments [Line Items]
Total agency MBS, at fair value		$ 573	$ 112
Weighted average coupon	[1]	3.05%	3.52%
Weighted average yield	[2]	2.66%	1.87%
Ginnie Mae [Member] | Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Agency MBS, par		$ 559	$ 107
Unamortized discount		0	0
Unamortized premium		8	2
Amortized cost		567	109
Gross unrealized gains		6	3
Gross unrealized losses		0	0
Total available-for-sale agency MBS, at fair value		573	112
Ginnie Mae [Member] | Agency securities remeasured at fair value through earnings [Member]
Schedule of Investments [Line Items]
Interest-only and principal-only strips, amortized cost		0	0
Gross unrealized gains		0	0
Gross unrealized losses		0	0
Total agency MBS measured at fair value through earnings		$ 0	$ 0

[1] The underlying unamortized principal balance ("UPB" or "par value") of our interest-only agency MBS strips was $1.0 billion and the weighted average contractual interest we are entitled to receive was 5.42% of this amount as of September 30, 2015. The par value of our principal-only agency MBS strips was $216 million as of September 30, 2015.

[2] Incorporates a weighted average future constant prepayment rate assumption of 9% based on forward rates as of September 30, 2015