Indebtedness - Advance and Warehouse Facilities Summary (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Debt Outstanding	$ 7,379,000,000	$ 6,763,000,000
Originations | Mortgage loans held for sale
Debt Instrument [Line Items]
Collateral Pledged	6,210,000,000	5,447,000,000
Debt Outstanding	5,970,000,000	5,330,000,000
Originations | Reverse mortgage interests
Debt Instrument [Line Items]
Collateral Pledged	614,000,000	606,000,000
Debt Outstanding	510,000,000	505,000,000
Originations | MSR
Debt Instrument [Line Items]
Collateral Pledged	1,827,000,000	1,217,000,000
Debt Outstanding	270,000,000	270,000,000
Advance Facilities | Servicing | Loans payable | $875 advance facility
Debt Instrument [Line Items]
Capacity Amount	875,000,000
Debt outstanding, gross	140,000,000	168,000,000
Collateral Pledged	$ 165,000,000	195,000,000
Advance Facilities | Servicing | Loans payable | $875 advance facility | CP rate | Minimum
Debt Instrument [Line Items]
Basis spread on rate	2.00%
Advance Facilities | Servicing | Loans payable | $875 advance facility | CP rate | Maximum
Debt Instrument [Line Items]
Basis spread on rate	6.50%
Advance Facilities | Servicing | Loans payable | $425 advance facility
Debt Instrument [Line Items]
Capacity Amount	$ 425,000,000
Debt outstanding, gross	197,000,000	192,000,000
Collateral Pledged	$ 250,000,000	246,000,000
Advance Facilities | Servicing | Loans payable | $425 advance facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Advance Facilities | Servicing | Loans payable | $425 advance facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	6.50%
Advance Facilities | Servicing | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 638,000,000	669,000,000
Collateral Pledged	806,000,000	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	70,000,000	74,000,000
Collateral Pledged	$ 92,000,000	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	$ 6,480,000,000	5,835,000,000
Collateral Pledged	6,824,000,000	6,053,000,000
Warehouse Facilities | Originations | Notes payable to banks | $2,000 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	2,000,000,000
Debt outstanding, gross	940,000,000	339,000,000
Collateral Pledged	$ 1,055,000,000	392,000,000
Warehouse Facilities | Originations | Notes payable to banks | $2,000 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Warehouse Facilities | Originations | Notes payable to banks | $2,000 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.00%
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,500,000,000
Debt outstanding, gross	867,000,000	1,081,000,000
Collateral Pledged	$ 838,000,000	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	1,442,000,000	1,003,000,000
Collateral Pledged	$ 1,495,000,000	1,037,000,000
Warehouse Facilities | Originations | Notes payable to banks | $2,500 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.60%
Warehouse Facilities | Originations | Notes payable to banks | $2,500 warehouse facility | LIBOR | Maximum
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	$ 1,350,000,000
Debt outstanding, gross	918,000,000	1,067,000,000
Collateral Pledged	$ 990,000,000	1,128,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,350 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.70%
Warehouse Facilities | Originations | Notes payable to banks | $1,350 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	3.90%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,200,000,000
Debt outstanding, gross	497,000,000	787,000,000
Collateral Pledged	$ 543,000,000	839,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility | LIBOR | Maximum
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	$ 750,000,000
Debt outstanding, gross	535,000,000	562,000,000
Collateral Pledged	$ 549,000,000	574,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.70%
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.80%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 750,000,000
Debt outstanding, gross	612,000,000	477,000,000
Collateral Pledged	$ 631,000,000	492,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.30%
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 600,000,000
Debt outstanding, gross	332,000,000	187,000,000
Collateral Pledged	$ 374,000,000	222,000,000
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 500,000,000
Debt outstanding, gross	0	0
Collateral Pledged	$ 0	0
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility | LIBOR | Maximum
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	129,000,000	163,000,000
Collateral Pledged	$ 130,000,000	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 | $250 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 250,000,000
Debt outstanding, gross	1,000,000	0
Collateral Pledged	$ 1,000,000	0
Warehouse Facilities | Originations | Notes payable to banks | $250 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.40%
Warehouse Facilities | Originations | Notes payable to banks | $250 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.30%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	169,000,000	131,000,000
Collateral Pledged	$ 173,000,000	134,000,000
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $50 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 50,000,000
Debt outstanding, gross	36,000,000	37,000,000
Collateral Pledged	$ 43,000,000	42,000,000
Warehouse Facilities | Originations | Notes payable to banks | $50 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $50 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	4.80%
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	2,000,000	1,000,000
Collateral Pledged	$ 2,000,000	1,000,000
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	$ 1,500,000,000
MSR Facilities | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	270,000,000	270,000,000
Collateral Pledged	1,827,000,000	1,217,000,000
MSR Facilities | Originations | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Debt outstanding, gross	0	0
Collateral Pledged	$ 471,000,000	247,000,000
MSR Facilities | Originations | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.50%
MSR Facilities | Originations | Notes payable to banks | $150 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 150,000,000
Debt outstanding, gross	0	0
Collateral Pledged	$ 438,000,000	228,000,000
MSR Facilities | Originations | Notes payable to banks | $150 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.80%
MSR Facilities | Originations | 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	$ 80,000,000	74,000,000
MSR Facilities | Originations | 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	$ 900,000,000
Advance Financing, Internally Allocated | Servicing | Loans payable | $640 advance facility
Debt Instrument [Line Items]
Capacity Amount	640,000,000
Debt outstanding, gross	231,000,000	235,000,000
Collateral Pledged	$ 299,000,000	305,000,000
Advance Financing, Internally Allocated | Servicing | Loans payable | $640 advance facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.90%
MSR Financing, Internally Allocated | Originations | 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	$ 838,000,000	668,000,000
MSR Financing, Internally Allocated | Originations | Notes payable to banks | $260 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.90%
Advance, Warehouse and MSR Facilities
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (9,000,000)	(11,000,000)
Debt Outstanding	7,379,000,000	6,763,000,000
Advance, Warehouse and MSR Facilities | Originations
Debt Instrument [Line Items]
Debt outstanding, gross	7,388,000,000	6,774,000,000
Collateral Pledged	$ 9,457,000,000	$ 8,114,000,000