SECURITIES - Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	$ 72,235,638	$ 65,793,672
Remaining Premium	3,661,219	3,771,429
Remaining Discount	(381,912)	(77,850)
Amortized Cost	63,746,389	62,903,483
Unrealized Gains	54,836	1,425,965
Unrealized Losses	(4,758,491)	(673,774)
Estimated Fair Value	59,042,734	63,655,674
Total Residential Securities
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	71,761,115	65,260,601
Remaining Premium	3,661,219	3,771,429
Remaining Discount	(380,136)	(77,723)
Amortized Cost	63,273,642	62,370,539
Unrealized Gains	54,836	1,425,800
Unrealized Losses	(4,742,770)	(671,170)
Estimated Fair Value	58,585,708	63,125,169
Agency
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	65,704,004	62,472,356
Remaining Premium	3,619,469	3,745,824
Remaining Discount	(282,071)	(20,438)
Amortized Cost	60,127,876	59,794,582
Unrealized Gains	40,213	1,386,383
Unrealized Losses	(4,574,753)	(655,360)
Estimated Fair Value	55,593,336	60,525,605
Agency | Fixed-rate pass-through
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	55,460,523	54,432,252
Remaining Premium	2,874,749	3,008,185
Remaining Discount	(281,278)	(18,314)
Amortized Cost	58,053,994	57,422,123
Unrealized Gains	31,761	1,349,125
Unrealized Losses	(4,306,637)	(474,643)
Estimated Fair Value	53,779,118	58,296,605
Agency | Adjustable-rate pass-through
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	260,238	305,211
Remaining Premium	10,651	1,965
Remaining Discount	(270)	(2,124)
Amortized Cost	270,619	305,052
Unrealized Gains	5,183	16,223
Unrealized Losses	(6,292)	(2)
Estimated Fair Value	269,510	321,273
Agency | CMO
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	106,189	114,533
Remaining Premium	1,848	1,888
Remaining Discount	0	0
Amortized Cost	108,037	116,421
Unrealized Gains	0	5,277
Unrealized Losses	(6,692)	0
Estimated Fair Value	101,345	121,698
Agency | Interest-only
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	1,662,567	1,912,415
Remaining Premium	416,404	456,683
Remaining Discount	0	0
Amortized Cost	416,404	456,683
Unrealized Gains	673	428
Unrealized Losses	(196,588)	(163,197)
Estimated Fair Value	220,489	293,914
Agency | Multifamily
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	8,182,519	5,671,138
Remaining Premium	312,441	273,553
Remaining Discount	(523)	0
Amortized Cost	1,243,478	1,453,946
Unrealized Gains	2,596	15,330
Unrealized Losses	(55,978)	(16,563)
Estimated Fair Value	1,190,096	1,452,713
Agency | Reverse mortgages
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	31,968	36,807
Remaining Premium	3,376	3,550
Remaining Discount	0	0
Amortized Cost	35,344	40,357
Unrealized Gains	0	0
Unrealized Losses	(2,566)	(955)
Estimated Fair Value	32,778	39,402
Agency | Multifamily Interest-Only Security
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	7,300,000	4,500,000
Residential credit
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	6,057,111	2,788,245
Remaining Premium	41,750	25,605
Remaining Discount	(98,065)	(57,285)
Amortized Cost	3,145,766	2,575,957
Unrealized Gains	14,623	39,417
Unrealized Losses	(168,017)	(15,810)
Estimated Fair Value	2,992,372	2,599,564
Residential credit | Credit risk transfer
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	1,010,209	924,101
Remaining Premium	6,552	8,754
Remaining Discount	(2,474)	(1,176)
Amortized Cost	1,014,287	927,555
Unrealized Gains	390	9,641
Unrealized Losses	(48,963)	(968)
Estimated Fair Value	965,714	936,228
Residential credit | Alt-A
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	138,473	83,213
Remaining Premium	33	31
Remaining Discount	(19,899)	(17,133)
Amortized Cost	118,607	66,111
Unrealized Gains	1,902	3,627
Unrealized Losses	(4,931)	(251)
Estimated Fair Value	115,578	69,487
Residential credit | Prime
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	1,227,193	323,062
Remaining Premium	15,855	9,841
Remaining Discount	(25,681)	(14,757)
Amortized Cost	297,095	268,117
Unrealized Gains	4,989	10,853
Unrealized Losses	(32,367)	(3,529)
Estimated Fair Value	269,717	275,441
Residential credit | Subprime
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	187,969	170,671
Remaining Premium	221	349
Remaining Discount	(17,896)	(16,111)
Amortized Cost	170,294	154,909
Unrealized Gains	4,045	8,285
Unrealized Losses	(7,020)	(118)
Estimated Fair Value	167,319	163,076
Residential credit | NPL/RPL
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	1,300,169	987,415
Remaining Premium	1,275	950
Remaining Discount	(6,026)	(1,698)
Amortized Cost	1,295,418	986,667
Unrealized Gains	343	2,739
Unrealized Losses	(45,858)	(5,968)
Estimated Fair Value	1,249,903	983,438
Residential credit | Prime jumbo (>=2010 vintage)
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	2,193,098	299,783
Remaining Premium	17,814	5,680
Remaining Discount	(26,089)	(6,410)
Amortized Cost	250,065	172,598
Unrealized Gains	2,954	4,272
Unrealized Losses	(28,878)	(4,976)
Estimated Fair Value	224,141	171,894
Residential credit | CRT interest-only security
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	0	4,100
Residential credit | Prime interest-only
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	920,300	50,000
Residential credit | Prime Jumbo interest-only
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	1,900,000	126,500
Commercial Securities
Mortgage-Backed Securities Portfolio [Line Items]
Principal / Notional	474,523	533,071
Remaining Premium	0	0
Remaining Discount	(1,776)	(127)
Amortized Cost	472,747	532,944
Unrealized Gains	0	165
Unrealized Losses	(15,721)	(2,604)
Estimated Fair Value	$ 457,026	$ 530,505