MBS (Details) (USD $)	Jun. 30, 2012 Y	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
MBS
Minimum term of fixed rate mortgages underlying MBS (in years)	15
Information about MBS
Principal/ Current Face	$ 12,903,367,000		$ 12,155,624,000
Purchase Premiums	191,546,000		178,904,000
Accretable Purchase Discounts	(265,241,000)		(250,614,000)
Discount Designated as Credit Reserve and OTTI	(1,440,752,000)		(1,228,766,000)
Amortized Cost	11,394,497,000		10,857,486,000
Carrying Value/ Fair Value	11,690,504,000		10,912,977,000
Gross Unrealized Gains	423,449,000		345,200,000
Gross Unrealized Losses	(127,442,000)		(289,709,000)
Net Unrealized Gain/(Loss)	296,007,000	312,954,000	55,491,000	292,376,000	403,185,000	393,822,000
Credit Reserve	1,388,000,000		1,174,000,000
OTTI	52,900,000		54,500,000
Principal payments receivable	5,600,000		2,300,000
Agency MBS
Information about MBS
Principal/ Current Face	6,619,530,000		6,741,271,000
Purchase Premiums	190,581,000		177,801,000
Accretable Purchase Discounts	(104,000)		(135,000)
Amortized Cost	6,815,584,000		6,921,275,000
Carrying Value/ Fair Value	7,014,611,000		7,137,531,000
Gross Unrealized Gains	201,894,000		218,000,000
Gross Unrealized Losses	(2,867,000)		(1,744,000)
Net Unrealized Gain/(Loss)	199,027,000		216,256,000
Agency MBS | Fannie Mae.
Information about MBS
Principal/ Current Face	5,914,532,000		5,981,834,000
Purchase Premiums	168,658,000		154,809,000
Accretable Purchase Discounts	(104,000)		(135,000)
Amortized Cost	6,083,086,000		6,136,508,000
Carrying Value/ Fair Value	6,256,800,000		6,329,925,000
Gross Unrealized Gains	176,532,000		194,997,000
Gross Unrealized Losses	(2,818,000)		(1,580,000)
Net Unrealized Gain/(Loss)	173,714,000		193,417,000
Agency MBS | Freddie Mac.
Information about MBS
Principal/ Current Face	689,648,000		743,517,000
Purchase Premiums	21,658,000		22,717,000
Amortized Cost	716,883,000		768,572,000
Carrying Value/ Fair Value	741,844,000		791,085,000
Gross Unrealized Gains	25,010,000		22,677,000
Gross Unrealized Losses	(49,000)		(164,000)
Net Unrealized Gain/(Loss)	24,961,000		22,513,000
Agency MBS | Ginnie Mae.
Information about MBS
Principal/ Current Face	15,350,000		15,920,000
Purchase Premiums	265,000		275,000
Amortized Cost	15,615,000		16,195,000
Carrying Value/ Fair Value	15,967,000		16,521,000
Gross Unrealized Gains	352,000		326,000
Net Unrealized Gain/(Loss)	352,000		326,000
Non-Agency MBS
Information about MBS
Principal/ Current Face	6,283,837,000		5,414,353,000
Purchase Premiums	965,000		1,103,000
Accretable Purchase Discounts	(265,137,000)		(250,479,000)
Discount Designated as Credit Reserve and OTTI	(1,440,752,000)		(1,228,766,000)
Amortized Cost	4,578,913,000		3,936,211,000
Carrying Value/ Fair Value	4,675,893,000		3,775,446,000
Gross Unrealized Gains	221,555,000		127,200,000
Gross Unrealized Losses	(124,575,000)		(287,965,000)
Net Unrealized Gain/(Loss)	96,980,000		(160,765,000)
Non-Agency MBS | Rated AAA
Information about MBS
Principal/ Current Face	38,015,000		12,258,000
Purchase Premiums	195,000		245,000
Accretable Purchase Discounts	(998,000)
Amortized Cost	37,212,000		12,503,000
Carrying Value/ Fair Value	37,150,000		12,258,000
Gross Unrealized Gains	52,000
Gross Unrealized Losses	(114,000)		(245,000)
Net Unrealized Gain/(Loss)	(62,000)		(245,000)
Non-Agency MBS | Rated AA
Information about MBS
Principal/ Current Face	47,000		47,000
Purchase Premiums	1,000		1,000
Amortized Cost	48,000		48,000
Carrying Value/ Fair Value	34,000		34,000
Gross Unrealized Losses	(14,000)		(14,000)
Net Unrealized Gain/(Loss)	(14,000)		(14,000)
Non-Agency MBS | Rated A
Information about MBS
Principal/ Current Face	22,836,000		28,950,000
Purchase Premiums	656,000		765,000
Accretable Purchase Discounts			(624,000)
Discount Designated as Credit Reserve and OTTI			(5,000)
Amortized Cost	23,492,000		29,086,000
Carrying Value/ Fair Value	20,895,000		24,911,000
Gross Unrealized Gains			341,000
Gross Unrealized Losses	(2,597,000)		(4,516,000)
Net Unrealized Gain/(Loss)	(2,597,000)		(4,175,000)
Non-Agency MBS | Rated BBB
Information about MBS
Principal/ Current Face	42,420,000		46,593,000
Purchase Premiums	56,000		42,000
Accretable Purchase Discounts	(2,874,000)		(3,020,000)
Discount Designated as Credit Reserve and OTTI	(499,000)		(582,000)
Amortized Cost	39,103,000		43,033,000
Carrying Value/ Fair Value	37,957,000		38,352,000
Gross Unrealized Gains	422,000
Gross Unrealized Losses	(1,568,000)		(4,681,000)
Net Unrealized Gain/(Loss)	(1,146,000)		(4,681,000)
Non-Agency MBS | Rated BB
Information about MBS
Principal/ Current Face	95,427,000		100,513,000
Purchase Premiums	41,000		33,000
Accretable Purchase Discounts	(6,358,000)		(10,749,000)
Discount Designated as Credit Reserve and OTTI	(1,653,000)		(3,223,000)
Amortized Cost	87,457,000		86,574,000
Carrying Value/ Fair Value	82,865,000		81,789,000
Gross Unrealized Gains	173,000		2,232,000
Gross Unrealized Losses	(4,765,000)		(7,017,000)
Net Unrealized Gain/(Loss)	(4,592,000)		(4,785,000)
Non-Agency MBS | Rated B
Information about MBS
Principal/ Current Face	319,951,000		355,930,000
Purchase Premiums	16,000		17,000
Accretable Purchase Discounts	(27,519,000)		(30,584,000)
Discount Designated as Credit Reserve and OTTI	(20,123,000)		(25,004,000)
Amortized Cost	272,325,000		300,359,000
Carrying Value/ Fair Value	269,844,000		277,438,000
Gross Unrealized Gains	8,596,000		2,729,000
Gross Unrealized Losses	(11,077,000)		(25,650,000)
Net Unrealized Gain/(Loss)	(2,481,000)		(22,921,000)
Non-Agency MBS | Rated CCC
Information about MBS
Principal/ Current Face	1,240,369,000		1,031,407,000
Accretable Purchase Discounts	(79,972,000)		(68,174,000)
Discount Designated as Credit Reserve and OTTI	(239,642,000)		(203,185,000)
Amortized Cost	920,755,000		760,048,000
Carrying Value/ Fair Value	960,116,000		741,028,000
Gross Unrealized Gains	55,757,000		27,767,000
Gross Unrealized Losses	(16,396,000)		(46,787,000)
Net Unrealized Gain/(Loss)	39,361,000		(19,020,000)
Non-Agency MBS | Rated CC
Information about MBS
Principal/ Current Face	578,202,000		687,664,000
Accretable Purchase Discounts	(28,951,000)		(33,478,000)
Discount Designated as Credit Reserve and OTTI	(108,941,000)		(142,777,000)
Amortized Cost	440,310,000		511,409,000
Carrying Value/ Fair Value	444,224,000		487,619,000
Gross Unrealized Gains	17,612,000		14,209,000
Gross Unrealized Losses	(13,698,000)		(37,999,000)
Net Unrealized Gain/(Loss)	3,914,000		(23,790,000)
Non-Agency MBS | Rated C
Information about MBS
Principal/ Current Face	1,710,909,000		2,128,919,000
Accretable Purchase Discounts	(57,740,000)		(64,963,000)
Discount Designated as Credit Reserve and OTTI	(385,361,000)		(487,397,000)
Amortized Cost	1,267,808,000		1,576,559,000
Carrying Value/ Fair Value	1,292,990,000		1,503,737,000
Gross Unrealized Gains	54,973,000		44,988,000
Gross Unrealized Losses	(29,791,000)		(117,810,000)
Net Unrealized Gain/(Loss)	25,182,000		(72,822,000)
Non-Agency MBS | Unrated and other
Information about MBS
Principal/ Current Face	2,235,661,000		1,022,072,000
Accretable Purchase Discounts	(60,725,000)		(38,887,000)
Discount Designated as Credit Reserve and OTTI	(684,533,000)		(366,593,000)
Amortized Cost	1,490,403,000		616,592,000
Carrying Value/ Fair Value	1,529,818,000		608,280,000
Gross Unrealized Gains	83,970,000		34,934,000
Gross Unrealized Losses	(44,555,000)		(43,246,000)
Net Unrealized Gain/(Loss)	39,415,000		(8,312,000)
Non-Agency MBS | D-rated
Information about MBS
Amortized Cost	1,476,000,000		602,000,000
Carrying Value/ Fair Value	$ 1,514,000,000		$ 593,800,000
Number of mortgage backed securities held	154		78