MBS (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013		Sep. 30, 2013		Dec. 31, 2012
Information about MBS
Minimum term of fixed rate mortgages underlying MBS			15 years
Principal/ Current Face	$ 12,284,174,000		$ 12,284,174,000		$ 13,302,328,000
Purchase Premiums	227,905,000		227,905,000		228,256,000
Accretable Purchase Discounts	(443,003,000)		(443,003,000)		(371,684,000)
Discount Designated as Credit Reserve and OTTI	(1,118,992,000)	[1]	(1,118,992,000)	[1]	(1,380,506,000)	[1]
Amortized Cost	10,953,504,000	[2]	10,953,504,000	[2]	11,782,817,000	[2]
Fair Value	11,671,067,000		11,671,067,000		12,607,625,000
Gross Unrealized Gains			793,983,000		832,560,000
Gross Unrealized Losses			(76,420,000)		(7,752,000)
Net Unrealized Gain/(Loss)			717,563,000		824,808,000
Principal payments receivable	3,400,000		3,400,000		4,400,000
Agency MBS
Information about MBS
Principal/ Current Face	6,418,511,000		6,418,511,000		6,792,768,000
Purchase Premiums	227,212,000		227,212,000		227,384,000
Accretable Purchase Discounts	(95,000)		(95,000)		(58,000)
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]	0	[1]
Amortized Cost	6,649,048,000	[2]	6,649,048,000	[2]	7,024,517,000	[2]
Fair Value	6,697,689,000		6,697,689,000		7,225,460,000
Gross Unrealized Gains			116,292,000		202,397,000
Gross Unrealized Losses			(67,651,000)		(1,454,000)
Net Unrealized Gain/(Loss)			48,641,000		200,943,000
Agency MBS | Fannie Mae.
Information about MBS
Principal/ Current Face	5,197,165,000		5,197,165,000		5,977,388,000
Purchase Premiums	180,854,000		180,854,000		196,686,000
Accretable Purchase Discounts	(95,000)		(95,000)		(58,000)
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]	0	[1]
Amortized Cost	5,377,924,000	[2]	5,377,924,000	[2]	6,174,016,000	[2]
Fair Value	5,440,656,000		5,440,656,000		6,351,621,000
Gross Unrealized Gains			104,702,000		178,970,000
Gross Unrealized Losses			(41,970,000)		(1,365,000)
Net Unrealized Gain/(Loss)			62,732,000		177,605,000
Agency MBS | Freddie Mac.
Information about MBS
Principal/ Current Face	1,208,358,000		1,208,358,000		800,854,000
Purchase Premiums	46,134,000		46,134,000		30,447,000
Accretable Purchase Discounts	0		0		0
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]	0	[1]
Amortized Cost	1,257,912,000	[2]	1,257,912,000	[2]	835,724,000	[2]
Fair Value	1,243,489,000		1,243,489,000		858,560,000
Gross Unrealized Gains			11,258,000		22,925,000
Gross Unrealized Losses			(25,681,000)		(89,000)
Net Unrealized Gain/(Loss)			(14,423,000)		22,836,000
Agency MBS | Ginnie Mae.
Information about MBS
Principal/ Current Face	12,988,000		12,988,000		14,526,000
Purchase Premiums	224,000		224,000		251,000
Accretable Purchase Discounts	0		0		0
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]	0	[1]
Amortized Cost	13,212,000	[2]	13,212,000	[2]	14,777,000	[2]
Fair Value	13,544,000		13,544,000		15,279,000
Gross Unrealized Gains			332,000		502,000
Gross Unrealized Losses			0		0
Net Unrealized Gain/(Loss)			332,000		502,000
Non-Agency MBS
Information about MBS
Principal/ Current Face	5,865,663,000	[3]	5,865,663,000	[3]	6,509,560,000	[3]
Purchase Premiums	693,000	[3]	693,000	[3]	872,000	[3]
Accretable Purchase Discounts	(442,908,000)	[3]	(442,908,000)	[3]	(371,626,000)	[3]
Discount Designated as Credit Reserve and OTTI	(1,118,992,000)	[1],[3]	(1,118,992,000)	[1],[3]	(1,380,506,000)	[1],[3]
Amortized Cost	4,304,456,000	[2],[3]	4,304,456,000	[2],[3]	4,758,300,000	[2],[3]
Fair Value	4,973,378,000	[3]	4,973,378,000	[3]	5,382,165,000	[3]
Gross Unrealized Gains			677,691,000	[3]	630,163,000	[3]
Gross Unrealized Losses			(8,769,000)	[3]	(6,298,000)	[3]
Net Unrealized Gain/(Loss)			668,922,000	[3]	623,865,000	[3]
Credit Reserve	1,074,000,000				1,332,000,000
OTTI	45,000,000		45,000,000		48,700,000
Non-Agency MBS | Rated AAA
Information about MBS
Principal/ Current Face	16,889,000	[3]	16,889,000	[3]	25,209,000	[3]
Purchase Premiums	85,000	[3]	85,000	[3]	158,000	[3]
Accretable Purchase Discounts	(177,000)	[3]	(177,000)	[3]	(219,000)	[3]
Discount Designated as Credit Reserve and OTTI	0	[1],[3]	0	[1],[3]	0	[1],[3]
Amortized Cost	16,797,000	[2],[3]	16,797,000	[2],[3]	25,148,000	[2],[3]
Fair Value	17,180,000	[3]	17,180,000	[3]	25,905,000	[3]
Gross Unrealized Gains			383,000	[3]	757,000	[3]
Gross Unrealized Losses			0	[3]	0	[3]
Net Unrealized Gain/(Loss)			383,000	[3]	757,000	[3]
Non-Agency MBS | Rated A
Information about MBS
Principal/ Current Face	698,000	[3]	698,000	[3]	1,147,000	[3]
Purchase Premiums	15,000	[3]	15,000	[3]	24,000	[3]
Accretable Purchase Discounts	0	[3]	0	[3]	0	[3]
Discount Designated as Credit Reserve and OTTI	0	[1],[3]	0	[1],[3]	0	[1],[3]
Amortized Cost	713,000	[2],[3]	713,000	[2],[3]	1,171,000	[2],[3]
Fair Value	681,000	[3]	681,000	[3]	1,086,000	[3]
Gross Unrealized Gains			0	[3]	0	[3]
Gross Unrealized Losses			(32,000)	[3]	(85,000)	[3]
Net Unrealized Gain/(Loss)			(32,000)	[3]	(85,000)	[3]
Non-Agency MBS | Rated BBB
Information about MBS
Principal/ Current Face	46,717,000	[3]	46,717,000	[3]	49,301,000	[3]
Purchase Premiums	536,000	[3]	536,000	[3]	637,000	[3]
Accretable Purchase Discounts	(1,182,000)	[3]	(1,182,000)	[3]	(1,741,000)	[3]
Discount Designated as Credit Reserve and OTTI	0	[1],[3]	0	[1],[3]	(378,000)	[1],[3]
Amortized Cost	46,071,000	[2],[3]	46,071,000	[2],[3]	47,819,000	[2],[3]
Fair Value	46,645,000	[3]	46,645,000	[3]	48,563,000	[3]
Gross Unrealized Gains			1,434,000	[3]	1,806,000	[3]
Gross Unrealized Losses			(860,000)	[3]	(1,062,000)	[3]
Net Unrealized Gain/(Loss)			574,000	[3]	744,000	[3]
Non-Agency MBS | Rated BB
Information about MBS
Principal/ Current Face	104,253,000	[3]	104,253,000	[3]	118,031,000	[3]
Purchase Premiums	45,000	[3]	45,000	[3]	39,000	[3]
Accretable Purchase Discounts	(7,734,000)	[3]	(7,734,000)	[3]	(8,892,000)	[3]
Discount Designated as Credit Reserve and OTTI	(861,000)	[1],[3]	(861,000)	[1],[3]	(853,000)	[1],[3]
Amortized Cost	95,703,000	[2],[3]	95,703,000	[2],[3]	108,325,000	[2],[3]
Fair Value	100,228,000	[3]	100,228,000	[3]	112,905,000	[3]
Gross Unrealized Gains			4,746,000	[3]	4,937,000	[3]
Gross Unrealized Losses			(221,000)	[3]	(357,000)	[3]
Net Unrealized Gain/(Loss)			4,525,000	[3]	4,580,000	[3]
Non-Agency MBS | Rated B
Information about MBS
Principal/ Current Face	273,241,000	[3]	273,241,000	[3]	247,532,000	[3]
Purchase Premiums	0	[3]	0	[3]	0	[3]
Accretable Purchase Discounts	(33,804,000)	[3]	(33,804,000)	[3]	(31,133,000)	[3]
Discount Designated as Credit Reserve and OTTI	(7,003,000)	[1],[3]	(7,003,000)	[1],[3]	(12,462,000)	[1],[3]
Amortized Cost	232,434,000	[2],[3]	232,434,000	[2],[3]	203,937,000	[2],[3]
Fair Value	257,247,000	[3]	257,247,000	[3]	225,281,000	[3]
Gross Unrealized Gains			24,859,000	[3]	21,452,000	[3]
Gross Unrealized Losses			(46,000)	[3]	(108,000)	[3]
Net Unrealized Gain/(Loss)			24,813,000	[3]	21,344,000	[3]
Non-Agency MBS | Rated CCC
Information about MBS
Principal/ Current Face	1,244,536,000	[3]	1,244,536,000	[3]	1,235,638,000	[3]
Purchase Premiums	12,000	[3]	12,000	[3]	14,000	[3]
Accretable Purchase Discounts	(135,061,000)	[3]	(135,061,000)	[3]	(107,618,000)	[3]
Discount Designated as Credit Reserve and OTTI	(190,357,000)	[1],[3]	(190,357,000)	[1],[3]	(201,126,000)	[1],[3]
Amortized Cost	919,130,000	[2],[3]	919,130,000	[2],[3]	926,908,000	[2],[3]
Fair Value	1,084,830,000	[3]	1,084,830,000	[3]	1,055,757,000	[3]
Gross Unrealized Gains			168,233,000	[3]	131,826,000	[3]
Gross Unrealized Losses			(2,533,000)	[3]	(2,977,000)	[3]
Net Unrealized Gain/(Loss)			165,700,000	[3]	128,849,000	[3]
Non-Agency MBS | Rated CC
Information about MBS
Principal/ Current Face	384,617,000	[3]	384,617,000	[3]	579,632,000	[3]
Purchase Premiums	0	[3]	0	[3]	0	[3]
Accretable Purchase Discounts	(36,426,000)	[3]	(36,426,000)	[3]	(41,191,000)	[3]
Discount Designated as Credit Reserve and OTTI	(87,400,000)	[1],[3]	(87,400,000)	[1],[3]	(132,061,000)	[1],[3]
Amortized Cost	260,791,000	[2],[3]	260,791,000	[2],[3]	406,380,000	[2],[3]
Fair Value	309,776,000	[3]	309,776,000	[3]	468,017,000	[3]
Gross Unrealized Gains			49,017,000	[3]	61,739,000	[3]
Gross Unrealized Losses			(32,000)	[3]	(102,000)	[3]
Net Unrealized Gain/(Loss)			48,985,000	[3]	61,637,000	[3]
Non-Agency MBS | Rated C
Information about MBS
Principal/ Current Face	340,721,000	[3]	340,721,000	[3]	952,984,000	[3]
Purchase Premiums	0	[3]	0	[3]	0	[3]
Accretable Purchase Discounts	(40,131,000)	[3]	(40,131,000)	[3]	(55,294,000)	[3]
Discount Designated as Credit Reserve and OTTI	(49,164,000)	[1],[3]	(49,164,000)	[1],[3]	(166,529,000)	[1],[3]
Amortized Cost	251,426,000	[2],[3]	251,426,000	[2],[3]	731,161,000	[2],[3]
Fair Value	297,497,000	[3]	297,497,000	[3]	812,523,000	[3]
Gross Unrealized Gains			46,252,000	[3]	81,850,000	[3]
Gross Unrealized Losses			(181,000)	[3]	(488,000)	[3]
Net Unrealized Gain/(Loss)			46,071,000	[3]	81,362,000	[3]
Non-Agency MBS | Unrated and D-rated
Information about MBS
Principal/ Current Face	3,453,991,000	[3],[4]	3,453,991,000	[3],[4]	3,300,086,000	[3],[4]
Purchase Premiums	0	[3],[4]	0	[3],[4]	0	[3],[4]
Accretable Purchase Discounts	(188,393,000)	[3],[4]	(188,393,000)	[3],[4]	(125,538,000)	[3],[4]
Discount Designated as Credit Reserve and OTTI	(784,207,000)	[1],[3],[4]	(784,207,000)	[1],[3],[4]	(867,097,000)	[1],[3],[4]
Amortized Cost	2,481,391,000	[2],[3],[4]	2,481,391,000	[2],[3],[4]	2,307,451,000	[2],[3],[4]
Fair Value	2,859,294,000	[3],[4]	2,859,294,000	[3],[4]	2,632,128,000	[3],[4]
Gross Unrealized Gains			382,767,000	[3],[4]	325,796,000	[3],[4]
Gross Unrealized Losses			(4,864,000)	[3],[4]	(1,119,000)	[3],[4]
Net Unrealized Gain/(Loss)			377,903,000	[3],[4]	324,677,000	[3],[4]
Non-Agency MBS | Rated D
Information about MBS
Amortized Cost	2,436,000,000		2,436,000,000		2,252,000,000
Fair Value	$ 2,805,000,000		$ 2,805,000,000		$ 2,573,000,000

[1] Discount designated as Credit Reserve and amounts related to OTTI are generally not expected to be accreted into interest income. Amounts disclosed at September 30, 2013 reflect Credit Reserve of $1.074 billion and OTTI of $45.0 million. Amounts disclosed at December 31, 2012 reflect Credit Reserve of $1.332 billion and OTTI of $48.7 million.

[2] Includes principal payments receivable of $3.4 million and $4.4 million at September 30, 2013 and December 31, 2012, respectively, which are not included in the Principal/Current Face.

[3] Non-Agency MBS, including Non-Agency MBS transferred to consolidated VIEs, are reported based on the lowest rating issued by a Rating Agency, if more than one rating is issued on the security, at the date presented.

[4] Includes Non-Agency MBS that were D-rated and had an aggregate amortized cost and fair value of $2.436 billion and $2.805 billion, respectively, at September 30, 2013 and Non-Agency MBS that were D-rated and had an aggregate amortized cost and fair value of $2.252 billion and $2.573 billion, respectively, at December 31, 2012.