Indebtedness - Notes Payable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Outstanding debt	$ 6,763,000,000	$ 4,997,000,000
Advance, Warehouse and MSR Facilities
Debt Instrument [Line Items]
Unamortized debt issuance costs	(11,000,000)	(1,000,000)
Outstanding debt	6,763,000,000	4,997,000,000
Servicing | Advance Facilities
Debt Instrument [Line Items]
Outstanding	669,000,000	422,000,000
Collateral Pledged	844,000,000	665,000,000
Originations | Warehouse Facilities
Debt Instrument [Line Items]
Outstanding	5,835,000,000	4,416,000,000
Collateral Pledged	6,053,000,000	4,622,000,000
Originations | MSR Facilities
Debt Instrument [Line Items]
Outstanding	270,000,000	160,000,000
Collateral Pledged	1,217,000,000	1,359,000,000
Originations | Advance, Warehouse and MSR Facilities
Debt Instrument [Line Items]
Outstanding	6,774,000,000	4,998,000,000
Collateral Pledged	8,114,000,000	6,646,000,000
Mortgage loans held for sale | Originations
Debt Instrument [Line Items]
Collateral Pledged	5,447,000,000	3,931,000,000
Outstanding debt	5,330,000,000	3,826,000,000
Reverse mortgage interests, net | Originations
Debt Instrument [Line Items]
Collateral Pledged	606,000,000	691,000,000
Outstanding debt	505,000,000	590,000,000
MSR | Originations
Debt Instrument [Line Items]
Collateral Pledged	1,217,000,000	1,359,000,000
Outstanding debt	270,000,000	160,000,000
Loans Payable | Servicing | $875 advance facility | Advance Facilities
Debt Instrument [Line Items]
Capacity Amount	875,000,000	125,000,000
Outstanding	168,000,000	37,000,000
Collateral Pledged	195,000,000	88,000,000
Loans Payable | Servicing | $640 advance facility | Advance Financing, Internally Allocated
Debt Instrument [Line Items]
Capacity Amount	640,000,000
Outstanding	235,000,000	0
Collateral Pledged	305,000,000	0
Loans Payable | Servicing | $425 advance facility | Advance Facilities
Debt Instrument [Line Items]
Capacity Amount	425,000,000	325,000,000
Outstanding	192,000,000	224,000,000
Collateral Pledged	246,000,000	285,000,000
Loans Payable | Servicing | $250 advance facility | Advance Facilities
Debt Instrument [Line Items]
Capacity Amount	250,000,000
Outstanding	0	98,000,000
Collateral Pledged	$ 0	167,000,000
Loans Payable | LIBOR | Servicing | $640 advance facility | Advance Financing, Internally Allocated
Debt Instrument [Line Items]
Interest Rate	3.90%
Loans Payable | Minimum | LIBOR | Servicing | $425 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	1.60%
Loans Payable | Minimum | LIBOR | Servicing | $250 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Loans Payable | Minimum | CPRATE | Servicing | $875 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	2.50%
Loans Payable | Maximum | LIBOR | Servicing | $250 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	2.60%
Loans Payable | Maximum | CPRATE | Servicing | $875 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	6.50%
Notes Payable to Banks | Servicing | $100 advance facility | Advance Facilities
Debt Instrument [Line Items]
Capacity Amount	$ 100,000,000
Outstanding	74,000,000	63,000,000
Collateral Pledged	98,000,000	125,000,000
Notes Payable to Banks | Originations | $2,000 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	2,000,000,000	200,000,000
Outstanding	339,000,000	54,000,000
Collateral Pledged	392,000,000	78,000,000
Notes Payable to Banks | Originations | $1,500 warehouse facility due June 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	1,500,000,000
Outstanding	1,081,000,000	759,000,000
Collateral Pledged	1,028,000,000	733,000,000
Notes Payable to Banks | Originations | $1,500 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	1,500,000,000	700,000,000
Outstanding	1,003,000,000	469,000,000
Collateral Pledged	1,037,000,000	488,000,000
Notes Payable to Banks | Originations | $1,350 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	1,350,000,000
Outstanding	1,067,000,000	589,000,000
Collateral Pledged	1,128,000,000	656,000,000
Notes Payable to Banks | Originations | $1,200 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	1,200,000,000
Outstanding	787,000,000	683,000,000
Collateral Pledged	839,000,000	724,000,000
Notes Payable to Banks | Originations | $750 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	750,000,000
Outstanding	562,000,000	411,000,000
Collateral Pledged	574,000,000	425,000,000
Notes Payable to Banks | Originations | $750 warehouse facility due August 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	750,000,000
Outstanding	477,000,000	0
Collateral Pledged	492,000,000	0
Notes Payable to Banks | Originations | $600 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	600,000,000
Outstanding	187,000,000	174,000,000
Collateral Pledged	222,000,000	202,000,000
Notes Payable to Banks | Originations | $500 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	500,000,000
Outstanding	0	336,000,000
Collateral Pledged	0	349,000,000
Notes Payable to Banks | Originations | $300 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	300,000,000
Outstanding	163,000,000	136,000,000
Collateral Pledged	164,000,000	136,000,000
Notes Payable to Banks | Originations | $250 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	250,000,000	1,000,000,000
Outstanding	0	762,000,000
Collateral Pledged	0	783,000,000
Notes Payable to Banks | Originations | $200 warehouse facility due April 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Outstanding	131,000,000	27,000,000
Collateral Pledged	134,000,000	27,000,000
Notes Payable to Banks | Originations | $200 warehouse facility due November 2020 | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Outstanding	0	0
Collateral Pledged	0	0
Notes Payable to Banks | Originations | $50 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	50,000,000
Outstanding	37,000,000	11,000,000
Collateral Pledged	42,000,000	15,000,000
Notes Payable to Banks | Originations | $40 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	40,000,000
Outstanding	1,000,000	5,000,000
Collateral Pledged	1,000,000	6,000,000
Notes Payable to Banks | Originations | $450 warehouse facility | MSR Facilities
Debt Instrument [Line Items]
Capacity Amount	450,000,000
Outstanding	0	150,000,000
Collateral Pledged	0	945,000,000
Notes Payable to Banks | Originations | $260 warehouse facility | MSR Financing, Internally Allocated
Debt Instrument [Line Items]
Capacity Amount	260,000,000
Outstanding	260,000,000	0
Collateral Pledged	668,000,000	0
Notes Payable to Banks | Originations | $200 warehouse facility due August 2021 | MSR Facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000	400,000,000
Outstanding	0	0
Collateral Pledged	247,000,000	200,000,000
Notes Payable to Banks | Originations | $150 warehouse facility | MSR Facilities
Debt Instrument [Line Items]
Capacity Amount	150,000,000
Outstanding	0	0
Collateral Pledged	228,000,000	130,000,000
Notes Payable to Banks | Originations | $50 warehouse facility due November 2022 | MSR Facilities
Debt Instrument [Line Items]
Capacity Amount	50,000,000
Outstanding	10,000,000	10,000,000
Collateral Pledged	74,000,000	84,000,000
Notes Payable to Banks | Originations | $900 warehouse facility | MSR Facilities
Debt Instrument [Line Items]
Capacity Amount	900,000,000
Notes Payable to Banks | Originations | $1,500 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Capacity Amount	$ 1,500,000,000	$ 800,000,000
Notes Payable to Banks | LIBOR | Servicing | $100 advance facility | Advance Facilities
Debt Instrument [Line Items]
Interest Rate	2.50%
Notes Payable to Banks | LIBOR | Originations | $2,000 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	2.30%
Notes Payable to Banks | LIBOR | Originations | $1,500 warehouse facility due June 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.70%
Notes Payable to Banks | LIBOR | Originations | $750 warehouse facility due August 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.80%
Notes Payable to Banks | LIBOR | Originations | $600 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	2.20%
Notes Payable to Banks | LIBOR | Originations | $300 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.40%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility due April 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.80%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility due November 2020 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.30%
Notes Payable to Banks | LIBOR | Originations | $40 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	3.30%
Notes Payable to Banks | LIBOR | Originations | $450 warehouse facility | MSR Facilities
Debt Instrument [Line Items]
Interest Rate	5.10%
Notes Payable to Banks | LIBOR | Originations | $260 warehouse facility | MSR Financing, Internally Allocated
Debt Instrument [Line Items]
Interest Rate	3.90%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility due August 2021 | MSR Facilities
Debt Instrument [Line Items]
Interest Rate	3.50%
Notes Payable to Banks | LIBOR | Originations | $150 warehouse facility | MSR Facilities
Debt Instrument [Line Items]
Interest Rate	3.80%
Notes Payable to Banks | LIBOR | Originations | $50 warehouse facility due November 2022 | MSR Facilities
Debt Instrument [Line Items]
Interest Rate	3.30%
Notes Payable to Banks | Minimum | LIBOR | Originations | $1,500 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.60%
Notes Payable to Banks | Minimum | LIBOR | Originations | $1,350 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.80%
Notes Payable to Banks | Minimum | LIBOR | Originations | $1,200 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.80%
Notes Payable to Banks | Minimum | LIBOR | Originations | $750 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.70%
Notes Payable to Banks | Minimum | LIBOR | Originations | $500 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	2.50%
Notes Payable to Banks | Minimum | LIBOR | Originations | $250 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.40%
Notes Payable to Banks | Minimum | LIBOR | Originations | $50 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.80%
Notes Payable to Banks | Maximum | LIBOR | Originations | $1,500 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	1.90%
Notes Payable to Banks | Maximum | LIBOR | Originations | $1,350 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	3.90%
Notes Payable to Banks | Maximum | LIBOR | Originations | $1,200 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	3.00%
Notes Payable to Banks | Maximum | LIBOR | Originations | $750 warehouse facility due October 2021 | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	2.80%
Notes Payable to Banks | Maximum | LIBOR | Originations | $500 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	4.00%
Notes Payable to Banks | Maximum | LIBOR | Originations | $250 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	2.30%
Notes Payable to Banks | Maximum | LIBOR | Originations | $50 warehouse facility | Warehouse Facilities
Debt Instrument [Line Items]
Interest Rate	4.80%