Investment Securities (Summary of Investment in Agency Security) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 30, 2011	Dec. 31, 2011		Dec. 31, 2010
Unrealized Gain On Derivative Instrument And Trading Securities	$ 17,000,000			$ 16,000,000		$ (1,000,000)
Unamortized premium	4,400,000,000			2,400,000,000
Amortized cost	82,652,000,000			53,503,000,000
Total agency MBS, at fair value	85,245,000,000			54,683,000,000
Weighted average coupon	3.69%	[1]		4.23%	[2]
Weighted average yield	2.61%	[3]		3.07%
Weighted average yield for the year ended	2.82%	[3]		3.19%
Unamortized principal balance of interest-only strips	1,700,000,000		1,100,000,000
Unamortized principal balance of principal-only strips	302,000,000		40,000,000
Weighted average contractual interest rate of interest only strips	5.78%		0.00%
Prepayment rate over remaining life of aggregate investment portfolio			14.00%
Average prepayment rate based on forward rate assumption	11.00%			14.00%
Average reset rate for adjustable rate securities	2.64%		2.71%
Average underlying index rate on agency securities based on current spot rate	0.93%		0.94%
Average Margin on agency securities	1.71%		1.77%
Fannie Mae [Member]
Total agency MBS, at fair value	64,190,000,000			39,689,000,000
Weighted average coupon	3.70%	[1]		4.18%	[2]
Weighted average yield	2.62%	[3]		3.03%
Weighted average yield for the year ended	2.83%	[3]		3.19%
Freddie Mac [Member]
Total agency MBS, at fair value	20,801,000,000			14,721,000,000
Weighted average coupon	3.67%	[1]		4.39%	[2]
Weighted average yield	2.61%	[3]		3.20%
Weighted average yield for the year ended	2.83%	[3]		3.20%
Ginnie Mae [Member]
Total agency MBS, at fair value	254,000,000			273,000,000
Weighted average coupon	3.77%	[1]		3.74%	[2]
Weighted average yield	1.60%	[3]		1.71%
Weighted average yield for the year ended	1.63%	[3]		2.05%
Available-for-sale Securities [Member]
Agency MBS, par	78,486,000,000			51,226,000,000
Unamortized premium	4,166,000,000			2,277,000,000
Amortized cost	82,652,000,000			53,503,000,000
Gross unrealized gains	2,072,000,000			1,007,000,000
Gross unrealized losses	(25,000,000)			(6,000,000)
Total available-for-sale agency MBS, at fair value	84,699,000,000			54,504,000,000
Available-for-sale Securities [Member] | Fannie Mae [Member]
Agency MBS, par	58,912,000,000			37,232,000,000
Unamortized premium	3,208,000,000			1,659,000,000
Amortized cost	62,120,000,000			38,891,000,000
Gross unrealized gains	1,585,000,000			680,000,000
Gross unrealized losses	(18,000,000)			(4,000,000)
Total available-for-sale agency MBS, at fair value	63,687,000,000			39,567,000,000
Available-for-sale Securities [Member] | Freddie Mac [Member]
Agency MBS, par	19,336,000,000			13,736,000,000
Unamortized premium	948,000,000			606,000,000
Amortized cost	20,284,000,000			14,342,000,000
Gross unrealized gains	481,000,000			324,000,000
Gross unrealized losses	(7,000,000)			(2,000,000)
Total available-for-sale agency MBS, at fair value	20,758,000,000			14,664,000,000
Available-for-sale Securities [Member] | Ginnie Mae [Member]
Agency MBS, par	238,000,000			258,000,000
Unamortized premium	10,000,000			12,000,000
Amortized cost	248,000,000			270,000,000
Gross unrealized gains	6,000,000			3,000,000
Gross unrealized losses	0			0
Total available-for-sale agency MBS, at fair value	254,000,000			273,000,000
Agency MBS remeasured at fair value through earnings [Member]
Interest-only and principal-only strips, amortized cost	541,000,000			191,000,000	[4]
Gross unrealized gains	27,000,000			9,000,000
Gross unrealized losses	(22,000,000)			(21,000,000)
Total agency MBS remeasured at fair value through earnings, at fair value	546,000,000			179,000,000
Agency MBS remeasured at fair value through earnings [Member] | Fannie Mae [Member]
Interest-only and principal-only strips, amortized cost	486,000,000			124,000,000	[4]
Gross unrealized gains	26,000,000			6,000,000
Gross unrealized losses	(9,000,000)			(8,000,000)
Total agency MBS remeasured at fair value through earnings, at fair value	503,000,000			122,000,000
Agency MBS remeasured at fair value through earnings [Member] | Freddie Mac [Member]
Interest-only and principal-only strips, amortized cost	55,000,000			67,000,000	[4]
Gross unrealized gains	1,000,000			3,000,000
Gross unrealized losses	(13,000,000)			(13,000,000)
Total agency MBS remeasured at fair value through earnings, at fair value	43,000,000			57,000,000
Agency MBS remeasured at fair value through earnings [Member] | Ginnie Mae [Member]
Interest-only and principal-only strips, amortized cost	0			0	[4]
Gross unrealized gains	0			0
Gross unrealized losses	0			0
Total agency MBS remeasured at fair value through earnings, at fair value	$ 0			$ 0

[1] The underlying unamortized principal balance (“UPB” or “par value”) of our interest-only agency MBS strips was $1.7 billion and the weighted average contractual interest we are entitled to receive was 5.78% of this amount as of December 31, 2012. The par value of our principal-only agency MBS strips was $302 million as of December 31, 2012.

[2] The weighted average coupon includes the interest cash flows from our interest-only securities taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO securities as a percentage of the par value of our agency securities (excluding the UPB of our interest-only securities) as of December 31, 2011.

[3] Incorporates a weighted average future constant prepayment rate assumption of 11% based on forward rates as of December 31, 2012 and a weighted average reset rate for adjustable rate securities of 2.64%, which is equal to a weighted average underlying index rate of 0.93% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.71%.

[4] The UPB of our interest-only securities was $1.1 billion and the weighted average contractual interest we are entitled to receive was 5.52% of this amount as of December 31, 2011. The par value of our principal-only agency MBS strips was $40 million as of December 31, 2011