DEBT OBLIGATIONS - Schedule of Debt Obligations (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Outstanding Face Amount	$ 31,033,899,000
Carrying Value	$ 31,008,077,000	$ 25,191,875,000
Weighted Average Funding Cost	1.72%
Weighted Average Life (Years)	1 year 1 month 6 days
MSR purchase price holdback	$ 45,983,000	44,623,000
Margin receivable, net	388,528,000	271,753,000
Secured Notes and Bonds Payable | Mr. Cooper
Debt Instrument [Line Items]
Outstanding Face Amount	5,800,000
Secured Financing Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	22,763,086,000
Carrying Value	$ 22,759,985,000	17,547,680,000
Weighted Average Funding Cost	1.31%
Weighted Average Life (Years)	6 months
MSR purchase price holdback	$ 65,700,000
Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	8,270,813,000
Carrying Value	$ 8,248,092,000	7,644,195,000
Weighted Average Funding Cost	2.87%
Weighted Average Life (Years)	2 years 8 months 12 days
Real Estate Owned
Debt Instrument [Line Items]
Weighted Average Funding Cost	2.91%
Warehouse Credit Facilities-Residential Mortgage Loans | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	$ 12,923,024,000
Carrying Value	$ 12,919,922,000	4,039,564,000
Weighted Average Funding Cost	2.01%
Weighted Average Life (Years)	9 months 18 days
Repurchase agreements	$ 266,400,000
Interest rate	4.00%
Warehouse Credit Facilities-Residential Mortgage Loans | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	23 years 10 months 24 days
Outstanding Face of Collateral	$ 13,774,859,000
Amortized Cost Basis of Collateral	13,775,860,000
Carrying Value of Collateral	13,803,756,000
Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Margin receivable, net	341,800,000
Agency RMBS | Secured Financing Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	8,956,064,000
Carrying Value	$ 8,956,064,000	12,682,427,000
Weighted Average Funding Cost	0.16%
Weighted Average Life (Years)	1 month 6 days
Agency RMBS | Secured Financing Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years 7 months 6 days
Outstanding Face of Collateral	$ 8,876,431,000
Amortized Cost Basis of Collateral	9,158,455,000
Carrying Value of Collateral	9,321,370,000
Non-Agency RMBS | Repurchase Agreements | Retained Servicer Advance and Consumer Bonds
Debt Instrument [Line Items]
Carrying Value	12,300,000
Non-Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Margin receivable, net	2,400,000
Non-Agency RMBS | Repurchase Agreements | Collateral | Retained Servicer Advance and Consumer Bonds
Debt Instrument [Line Items]
Carrying Value	16,500,000
Non-Agency RMBS | Secured Financing Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	723,486,000
Carrying Value	$ 723,486,000	817,209,000
Weighted Average Funding Cost	2.52%
Weighted Average Life (Years)	0 years
Non-Agency RMBS | Secured Financing Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	3 years 3 months 18 days
Outstanding Face of Collateral	$ 13,927,317,000
Amortized Cost Basis of Collateral	905,336,000
Carrying Value of Collateral	987,803,000
Real Estate Owned | Secured Financing Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	160,512,000
Carrying Value	$ 160,513,000	8,480,000
Weighted Average Life (Years)	1 year 2 months 12 days
Real Estate Owned | Secured Financing Agreements | Single Family Rental Collateralized Notes
Debt Instrument [Line Items]
Outstanding Face Amount	$ 152,600,000
Real Estate Owned | Secured Financing Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	4 years 6 months
Amortized Cost Basis of Collateral	$ 230,128,000
Carrying Value of Collateral	224,580,000
Excess MSRs
Debt Instrument [Line Items]
Carrying Value	248,061,000	275,088,000
Excess MSRs | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	248,061,000
Carrying Value	$ 248,061,000	275,088,000
Weighted Average Funding Cost	3.74%
Weighted Average Life (Years)	3 years 10 months 24 days
Excess MSRs | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years 3 months 18 days
Outstanding Face of Collateral	$ 84,829,582,000
Amortized Cost Basis of Collateral	281,142,000
Carrying Value of Collateral	348,080,000
MSRs | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	3,629,810,000
Carrying Value	$ 3,617,850,000	2,691,791,000
Weighted Average Funding Cost	3.69%
Weighted Average Life (Years)	3 years 2 months 12 days
MSRs | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years 1 month 6 days
Outstanding Face of Collateral	$ 531,851,913,000
Amortized Cost Basis of Collateral	6,029,066,000
Carrying Value of Collateral	6,477,289,000
Servicer Advance Investments | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	381,286,000
Carrying Value	$ 380,420,000	423,144,000
Weighted Average Funding Cost	1.30%
Weighted Average Life (Years)	1 year 1 month 6 days
Servicer Advance Investments | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years
Outstanding Face of Collateral	$ 408,085,000
Amortized Cost Basis of Collateral	453,442,000
Carrying Value of Collateral	$ 472,004,000
Servicer Advances | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	1.10%
Servicer Advances | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	1.90%
Servicer Advances | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 2,347,819,000
Carrying Value	$ 2,342,335,000	2,585,575,000
Weighted Average Funding Cost	2.34%
Weighted Average Life (Years)	1 year 4 months 24 days
Face amount of debt at fixed rate	$ 1,800,000,000
Servicer Advances | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	8 months 12 days
Outstanding Face of Collateral	$ 2,796,796,000
Amortized Cost Basis of Collateral	2,782,622,000
Carrying Value of Collateral	2,782,622,000
Residential Mortgage Loans | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	1,170,838,000
Carrying Value	$ 1,162,080,000	1,039,838,000
Weighted Average Funding Cost	2.10%
Weighted Average Life (Years)	3 years 7 months 6 days
Residential Mortgage Loans | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	20 years
Outstanding Face of Collateral	$ 1,192,146,000
Amortized Cost Basis of Collateral	1,311,940,000
Carrying Value of Collateral	1,313,998,000
Consumer Loans
Debt Instrument [Line Items]
Carrying Value	497,346,000	628,759,000
Consumer Loans | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	492,999,000
Carrying Value	$ 497,346,000	$ 628,759,000
Weighted Average Funding Cost	2.04%
Weighted Average Life (Years)	3 years 7 months 6 days
Consumer Loans | Secured Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	3 years 3 months 18 days
Outstanding Face of Collateral	$ 485,966,000
Amortized Cost Basis of Collateral	496,573,000
Carrying Value of Collateral	547,548,000
3.7% Secured Corporate Note | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 248,100,000
3.7% Secured Corporate Note | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	3.70%
2.8% To 4.5% Agency MSR Secured Note And Bond Payable | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Outstanding Face Amount	$ 1,300,000,000
2.8% To 4.5% Agency MSR Secured Note And Bond Payable | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	2.80%
2.8% To 4.5% Agency MSR Secured Note And Bond Payable | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	4.50%
3.9% Agency MSR | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	3.90%
3.9% Agency MSR | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 99,900,000
3.0% To 5.4% Public Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 2,200,000,000
3.0% To 5.4% Public Notes | Secured Notes and Bonds Payable | Minimum
Debt Instrument [Line Items]
Interest rate	3.00%
3.0% To 5.4% Public Notes | Secured Notes and Bonds Payable | Maximum
Debt Instrument [Line Items]
Interest rate	5.40%
2.9% Residential Mortgage Loans | Secured Notes and Bonds Payable | Mr. Cooper
Debt Instrument [Line Items]
Collateral amount	$ 1,600,000
2.9% Residential Mortgage Loans | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Mr. Cooper
Debt Instrument [Line Items]
Variable interest rate spread	2.90%
3.8% Asset-Backed Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 30,400,000
3.8% Asset-Backed Notes | Secured Notes and Bonds Payable | Maximum
Debt Instrument [Line Items]
Weighted Average Funding Cost	3.80%
6.6% Asset-Backed Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 46,500,000
Interest rate	6.60%
3.6% To 5.00% Asset-Backed Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 232,200,000
3.6% To 5.00% Asset-Backed Notes | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	3.60%
3.6% To 5.00% Asset-Backed Notes | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	5.00%
2.8% Asset-Backed Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 105,800,000
Interest rate	2.75%
Revolving Warehouse Facility Backed Notes | Secured Notes and Bonds Payable | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	1.13%
Revolving Warehouse Facility Backed Notes | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 750,000,000
Consumer Loan, UPB Class A | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Interest rate	2.00%
Residential mortgage loan UPB	$ 440,000,000
Consumer Loan, UPB Class B | Secured Notes and Bonds Payable
Debt Instrument [Line Items]
Interest rate	2.70%
Residential mortgage loan UPB	$ 53,000,000