MBS and CRT Securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Schedule of MBS and CRT Securities [Line Items]
Minimum term of fixed rate mortgages underlying MBS		15 years
Principal/ Current Face	$ 11,964,508	$ 11,964,508	$ 11,039,694
Purchase Premiums	181,038	181,038	213,790
Accretable Purchase Discounts	(340,840)	(340,840)	(404,362)
Discount Designated as Credit Reserve and OTTI	(815,397)	(815,397)	(900,557)
Amortized Cost	10,990,421	10,990,421	9,949,107
Fair Value	11,694,667	11,694,667	10,762,622
Gross Unrealized Gains	738,219	738,219	852,963
Gross Unrealized Losses	(33,974)	(33,974)	(39,448)
Net Unrealized Gain/(Loss)	704,245	704,245	813,515
Principal payments receivable	1,100	1,100	542
Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face			1,926,987
Amortized Cost			1,913,276
Fair Value			1,917,813
Total MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	11,808,508	11,808,508	10,930,194
Purchase Premiums	181,038	181,038	213,790
Accretable Purchase Discounts	(335,768)	(335,768)	(399,635)
Discount Designated as Credit Reserve and OTTI	(815,397)	(815,397)	(900,557)
Amortized Cost	10,839,493	10,839,493	9,844,334
Fair Value	11,544,699	11,544,699	10,659,639
Gross Unrealized Gains	737,431	737,431	852,639
Gross Unrealized Losses	(32,226)	(32,226)	(37,334)
Net Unrealized Gain/(Loss)	705,205	705,205	815,305
Agency Mortgage Backed Securities
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	4,772,899	4,772,899	5,610,293
Purchase Premiums	180,806	180,806	213,329
Accretable Purchase Discounts	(61)	(61)	(71)
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	4,954,756	4,954,756	5,824,093
Fair Value	5,020,477	5,020,477	5,904,207
Gross Unrealized Gains	88,541	88,541	113,736
Gross Unrealized Losses	(22,820)	(22,820)	(33,622)
Net Unrealized Gain/(Loss)	65,721	65,721	80,114
Agency Mortgage Backed Securities | Fannie Mae
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	3,875,329	3,875,329	4,587,823
Purchase Premiums	146,519	146,519	174,245
Accretable Purchase Discounts	(61)	(61)	(71)
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	4,021,787	4,021,787	4,761,997
Fair Value	4,086,523	4,086,523	4,843,084
Gross Unrealized Gains	79,498	79,498	102,187
Gross Unrealized Losses	(14,762)	(14,762)	(21,100)
Net Unrealized Gain/(Loss)	64,736	64,736	81,087
Agency Mortgage Backed Securities | Freddie Mac
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	887,904	887,904	1,011,659
Purchase Premiums	34,118	34,118	38,895
Accretable Purchase Discounts	0	0	0
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	923,134	923,134	1,051,096
Fair Value	923,872	923,872	1,049,854
Gross Unrealized Gains	8,796	8,796	11,280
Gross Unrealized Losses	(8,058)	(8,058)	(12,522)
Net Unrealized Gain/(Loss)	738	738	(1,242)
Agency Mortgage Backed Securities | Ginnie Mae
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	9,666	9,666	10,811
Purchase Premiums	169	169	189
Accretable Purchase Discounts	0	0	0
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	9,835	9,835	11,000
Fair Value	10,082	10,082	11,269
Gross Unrealized Gains	247	247	269
Gross Unrealized Losses	0	0	0
Net Unrealized Gain/(Loss)	247	247	269
Non-Agency MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	7,035,609	7,035,609	5,319,901
Purchase Premiums	232	232	461
Accretable Purchase Discounts	(335,707)	(335,707)	(399,564)
Discount Designated as Credit Reserve and OTTI	(815,397)	(815,397)	(900,557)
Amortized Cost	5,884,737	5,884,737	4,020,241
Fair Value	6,524,222	6,524,222	4,755,432
Gross Unrealized Gains	648,890	648,890	738,903
Gross Unrealized Losses	(9,406)	(9,406)	(3,712)
Net Unrealized Gain/(Loss)	639,484	639,484	735,191
Credit Reserve		793,700	877,600
OTTI	21,700	21,700	23,000
Non-Agency MBS | Expected to Recover Par
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	2,764,021	2,764,021	431,788
Purchase Premiums	232	232	461
Accretable Purchase Discounts	(31,691)	(31,691)	(29,501)
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	2,732,562	2,732,562	402,748
Fair Value	2,755,036	2,755,036	428,431
Gross Unrealized Gains	27,326	27,326	26,735
Gross Unrealized Losses	(4,853)	(4,853)	(1,052)
Net Unrealized Gain/(Loss)	22,473	22,473	25,683
Non-Agency MBS | Expected to Recover Less Than Par
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	4,271,588	4,271,588	4,888,113
Purchase Premiums	0	0	0
Accretable Purchase Discounts	(304,016)	(304,016)	(370,063)
Discount Designated as Credit Reserve and OTTI	(815,397)	(815,397)	(900,557)
Amortized Cost	3,152,175	3,152,175	3,617,493
Fair Value	3,769,186	3,769,186	4,327,001
Gross Unrealized Gains	621,564	621,564	712,168
Gross Unrealized Losses	(4,553)	(4,553)	(2,660)
Net Unrealized Gain/(Loss)	$ 617,011	$ 617,011	$ 709,508
Percentage of current face amount of Non-Agency MBS to be recovered	88.00%	88.00%	83.00%
CRT securities
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	$ 156,000	$ 156,000	$ 109,500
Purchase Premiums	0	0	0
Accretable Purchase Discounts	(5,072)	(5,072)	(4,727)
Discount Designated as Credit Reserve and OTTI	0	0	0
Amortized Cost	150,928	150,928	104,773
Fair Value	149,968	149,968	102,983
Gross Unrealized Gains	788	788	324
Gross Unrealized Losses	(1,748)	(1,748)	(2,114)
Net Unrealized Gain/(Loss)	(960)	(960)	(1,790)
CRT securities | Fair value option elected, debt securities
Schedule of MBS and CRT Securities [Line Items]
Fair Value	27,700	27,700
Gross Unrealized Gains	515	515
Gross Unrealized Losses	(19)	(19)
Net Unrealized Gain/(Loss)	496	496
CRT securities | Fair value option elected, debt securities | Other income, net
Schedule of MBS and CRT Securities [Line Items]
Unrealized gains (losses), net	(14)	496
CRT securities | Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face			4,500
Amortized Cost			4,500
Fair Value			4,624
RPL/NPL MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	2,492,000	2,492,000	161,000
Amortized Cost	2,490,000	2,490,000	161,000
Fair Value	$ 2,487,000	$ 2,487,000	161,000
RPL/NPL MBS | Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face			1,849,974
Amortized Cost			1,847,118
Fair Value			$ 1,846,807