Indebtedness - Advance and Warehouse Facilities Summary (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Advance and warehouse facilities, net	$ 8,206,000,000	$ 6,258,000,000
Document Quarterly Report	true
Advance Facilities | Servicing | Loans payable | $350 advance facility(3)
Debt Instrument [Line Items]
Capacity Amount	$ 350,000,000	875,000,000
Debt outstanding, gross	136,000,000	168,000,000
Collateral Pledged	$ 159,000,000	195,000,000
Advance Facilities | Servicing | Loans payable | $350 advance facility(3) | CP rate | Min
Debt Instrument [Line Items]
Basis spread on rate	2.00%
Advance Facilities | Servicing | Loans payable | $350 advance facility(3) | CP rate | Max
Debt Instrument [Line Items]
Basis spread on rate	6.50%
Advance Facilities | Servicing | Loans payable | $640 advance facility
Debt Instrument [Line Items]
Capacity Amount	$ 350,000,000	425,000,000
Debt outstanding, gross	168,000,000	192,000,000
Collateral Pledged	$ 211,000,000	246,000,000
Advance Facilities | Servicing | Loans payable | $640 advance facility | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.10%
Advance Facilities | Servicing | Loans payable | $640 advance facility | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	6.50%
Advance Facilities | Servicing | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 539,000,000	669,000,000
Collateral Pledged	684,000,000	844,000,000
Advance Facilities | Servicing | Notes payable to banks | $100 advance facility
Debt Instrument [Line Items]
Capacity Amount	100,000,000
Debt outstanding, gross	65,000,000	74,000,000
Collateral Pledged	$ 86,000,000	98,000,000
Advance Facilities | Servicing | Notes payable to banks | $100 advance facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 7,375,000,000	5,330,000,000
Collateral Pledged	7,735,000,000	5,447,000,000
Warehouse Facilities | Originations | Notes payable to banks | $4,000 warehouse facility(4)
Debt Instrument [Line Items]
Capacity Amount	4,000,000,000	2,000,000,000
Debt outstanding, gross	3,117,000,000	339,000,000
Collateral Pledged	$ 3,352,000,000	392,000,000
Warehouse Facilities | Originations | Notes payable to banks | $4,000 warehouse facility(4) | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Warehouse Facilities | Originations | Notes payable to banks | $4,000 warehouse facility(4) | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	2.20%
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,500,000,000
Debt outstanding, gross	546,000,000	1,081,000,000
Collateral Pledged	$ 529,000,000	1,028,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $2,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 2,500,000,000	1,500,000,000
Debt outstanding, gross	1,225,000,000	1,003,000,000
Collateral Pledged	$ 1,276,000,000	1,037,000,000
Warehouse Facilities | Originations | Notes payable to banks | $2,500 warehouse facility | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Warehouse Facilities | Originations | Notes payable to banks | $2,500 warehouse facility | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	1.90%
Warehouse Facilities | Originations | Notes payable to banks | $1,350 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,600,000,000
Debt outstanding, gross	906,000,000	951,000,000
Collateral Pledged	$ 945,000,000	977,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,350 warehouse facility | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $1,350 warehouse facility | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	3.00%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility(6)
Debt Instrument [Line Items]
Capacity Amount	$ 1,200,000,000
Debt outstanding, gross	473,000,000	586,000,000
Collateral Pledged	$ 492,000,000	607,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility(6) | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility(6) | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	3.00%
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse
Debt Instrument [Line Items]
Capacity Amount	$ 500,000,000	750,000,000
Debt outstanding, gross	231,000,000	562,000,000
Collateral Pledged	$ 238,000,000	574,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 550,000,000	750,000,000
Debt outstanding, gross	84,000,000	477,000,000
Collateral Pledged	$ 86,000,000	492,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility(6)
Debt Instrument [Line Items]
Capacity Amount	$ 600,000,000
Debt outstanding, gross	37,000,000	0
Collateral Pledged	$ 38,000,000	0
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility(6) | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility(6)
Debt Instrument [Line Items]
Capacity Amount	$ 500,000,000
Debt outstanding, gross	125,000,000	0
Collateral Pledged	$ 125,000,000	0
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility(6) | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility(6) | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	4.00%
Warehouse Facilities | Originations | Notes payable to banks | $300 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 300,000,000
Debt outstanding, gross	94,000,000	163,000,000
Collateral Pledged	$ 96,000,000	164,000,000
Warehouse Facilities | Originations | Notes payable to banks | $300 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.40%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility(10)
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	3,000,000	131,000,000
Collateral Pledged	$ 3,000,000	134,000,000
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility(10) | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility(11)
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000	50,000,000
Debt outstanding, gross	47,000,000	37,000,000
Collateral Pledged	$ 54,000,000	42,000,000
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility(11) | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility(11) | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	4.90%
Warehouse Facilities | Originations | Notes payable to banks | $30 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 30,000,000	40,000,000
Debt outstanding, gross	0	0
Collateral Pledged	$ 0	0
Warehouse Facilities | Originations | Notes payable to banks | $30 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.30%
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 2,000,000,000	1,500,000,000
Warehouse Facilities | Originations | Notes payable to banks | $500 Million Warehouse Facility Due June 2023
Debt Instrument [Line Items]
Capacity Amount	500,000,000
Debt outstanding, gross	439,000,000	0
Collateral Pledged	$ 452,000,000	0
Warehouse Facilities | Originations | Notes payable to banks | $500 Million Warehouse Facility Due June 2023 | LIBOR | Min
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Warehouse Facilities | Originations | Notes payable to banks | $500 Million Warehouse Facility Due June 2023 | LIBOR | Max
Debt Instrument [Line Items]
Basis spread on rate	3.00%
Warehouse Facilities | Originations | Notes payable to banks | $500 Million Warehouse Facility Due August 2023
Debt Instrument [Line Items]
Capacity Amount	$ 500,000,000
Debt outstanding, gross	48,000,000	0
Collateral Pledged	$ 49,000,000	0
Warehouse Facilities | Originations | Notes payable to banks | $500 Million Warehouse Facility Due August 2023 | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.70%
MSR Facilities | Servicing | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 305,000,000	270,000,000
Collateral Pledged	2,295,000,000	1,217,000,000
MSR Facilities | Servicing | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	400,000,000	200,000,000
Debt outstanding, gross	35,000,000	0
Collateral Pledged	$ 685,000,000	247,000,000
MSR Facilities | Servicing | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.00%
MSR Facilities | Servicing | Notes payable to banks | $150 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 400,000,000	150,000,000
Debt outstanding, gross	0	0
Collateral Pledged	$ 601,000,000	228,000,000
MSR Facilities | Servicing | Notes payable to banks | $150 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.00%
MSR Facilities | Servicing | Notes payable to banks | $50 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 50,000,000
Debt outstanding, gross	10,000,000	10,000,000
Collateral Pledged	$ 69,000,000	74,000,000
MSR Facilities | Servicing | Notes payable to banks | $50 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.30%
MSR Facilities | Originations | Notes payable to banks | $900 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,200,000,000	900,000,000
Advance Financing, Internally Allocated | Servicing | Loans payable | $425 advance facility
Debt Instrument [Line Items]
Capacity Amount	940,000,000	640,000,000
Debt outstanding, gross	170,000,000	235,000,000
Collateral Pledged	$ 228,000,000	305,000,000
Advance Financing, Internally Allocated | Servicing | Loans payable | $425 advance facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.50%
MSR Financing, Internally Allocated | Servicing | Notes payable to banks | $260 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 260,000,000
Debt outstanding, gross	260,000,000	260,000,000
Collateral Pledged	$ 940,000,000	668,000,000
MSR Financing, Internally Allocated | Servicing | Notes payable to banks | $260 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.50%
MSR Financing, Internally Allocated | Originations | Notes payable to banks | $260 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 260,000,000	260,000,000
Advance, Warehouse and MSR Facilities
Debt Instrument [Line Items]
Debt outstanding, gross	8,219,000,000	6,269,000,000
Collateral Pledged	10,714,000,000	7,508,000,000
Unamortized debt issuance costs	(13,000,000)	(11,000,000)
Advance and warehouse facilities, net	$ 8,206,000,000	$ 6,258,000,000