Indebtedness - Notes Payable Summary (Details) - USD ($)	9 Months Ended
	Sep. 30, 2020	Oct. 31, 2020	Jun. 30, 2020	May 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt Outstanding	$ 4,851,000,000						$ 4,997,000,000
Originations | Mortgage loans held for sale
Debt Instrument [Line Items]
Collateral Pledged	3,637,000,000						3,931,000,000
Debt Outstanding	3,560,000,000						3,826,000,000
Originations | Reverse mortgage interests
Debt Instrument [Line Items]
Collateral Pledged	564,000,000						691,000,000
Debt Outstanding	468,000,000						590,000,000
Originations | MSR
Debt Instrument [Line Items]
Collateral Pledged	1,075,000,000						1,359,000,000
Debt Outstanding	266,000,000						160,000,000
Advance Facilities | Servicing
Debt Instrument [Line Items]
Debt outstanding, gross	569,000,000						422,000,000
Collateral Pledged	728,000,000						665,000,000
Advance Facilities | Servicing | Loans payable | $875 advance facility
Debt Instrument [Line Items]
Capacity Amount	875,000,000				$ 875,000,000	$ 125,000,000
Debt outstanding, gross	144,000,000						37,000,000
Collateral Pledged	$ 169,000,000						88,000,000
Advance Facilities | Servicing | Loans payable | $875 advance facility | CP rate | Minimum
Debt Instrument [Line Items]
Basis spread on rate	2.50%
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				$ 425,000,000	325,000,000
Debt outstanding, gross	206,000,000						224,000,000
Collateral Pledged	$ 261,000,000						285,000,000
Advance Facilities | Servicing | Loans payable | $425 advance facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	2.80%
Advance Facilities | Servicing | Loans payable | $425 advance facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	6.50%
Advance Facilities | Servicing | Loans payable | $250 advance facility
Debt Instrument [Line Items]
Capacity Amount	$ 250,000,000
Debt outstanding, gross	0						98,000,000
Collateral Pledged	$ 0						167,000,000
Advance Facilities | Servicing | Loans payable | $250 advance facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.50%
Advance Facilities | Servicing | Loans payable | $250 advance facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.60%
Advance Facilities | Servicing | Notes payable to banks | $100 advance facility
Debt Instrument [Line Items]
Capacity Amount	$ 100,000,000
Debt outstanding, gross	75,000,000						63,000,000
Collateral Pledged	$ 102,000,000						125,000,000
Advance Facilities | Servicing | Notes payable to banks | $100 advance facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations
Debt Instrument [Line Items]
Debt outstanding, gross	$ 4,028,000,000						4,416,000,000
Collateral Pledged	4,201,000,000						4,622,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	1,500,000,000
Debt outstanding, gross	666,000,000						759,000,000
Collateral Pledged	$ 634,000,000						733,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.70%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,200,000,000
Debt outstanding, gross	564,000,000						683,000,000
Collateral Pledged	$ 610,000,000						724,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.50%
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 | $1.050 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,050,000,000
Debt outstanding, gross	627,000,000						589,000,000
Collateral Pledged	$ 679,000,000						656,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1.050 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.80%
Warehouse Facilities | Originations | Notes payable to banks | $1.050 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	3.90%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 750,000,000
Debt outstanding, gross	574,000,000						0
Collateral Pledged	$ 591,000,000						0
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR
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	$ 750,000,000
Debt outstanding, gross	472,000,000						411,000,000
Collateral Pledged	$ 481,000,000						425,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.70%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.80%
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse
Debt Instrument [Line Items]
Capacity Amount	$ 750,000,000		$ 200,000,000
Debt outstanding, gross	105,000,000						54,000,000
Collateral Pledged	$ 135,000,000						78,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 million warehouse | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.30%
Warehouse Facilities | Originations | Notes payable to banks | $700 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 700,000,000
Debt outstanding, gross	488,000,000						469,000,000
Collateral Pledged	$ 505,000,000						488,000,000
Warehouse Facilities | Originations | Notes payable to banks | $700 warehouse facility | Subsequent Event
Debt Instrument [Line Items]
Capacity Amount		$ 1,500,000,000
Warehouse Facilities | Originations | Notes payable to banks | $700 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.30%
Warehouse Facilities | Originations | Notes payable to banks | $700 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	2.20%
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 600,000,000
Debt outstanding, gross	156,000,000						174,000,000
Collateral Pledged	$ 185,000,000						202,000,000
Warehouse Facilities | Originations | Notes payable to banks | $600 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.20%
Warehouse Facilities | Originations | Notes payable to banks | $500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 500,000,000
Debt outstanding, gross	0						336,000,000
Collateral Pledged	$ 0						349,000,000
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	258,000,000						136,000,000
Collateral Pledged	$ 258,000,000						136,000,000
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			$ 250,000,000		$ 1,000,000,000
Debt outstanding, gross	0						762,000,000
Collateral Pledged	$ 0						783,000,000
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	72,000,000						27,000,000
Collateral Pledged	$ 74,000,000						27,000,000
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 | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	0						0
Collateral Pledged	$ 0						0
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.30%
Warehouse Facilities | Originations | Notes payable to banks | $50 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 50,000,000
Debt outstanding, gross	43,000,000						11,000,000
Collateral Pledged	$ 45,000,000						15,000,000
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 | $40 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 40,000,000
Debt outstanding, gross	3,000,000						5,000,000
Collateral Pledged	$ 4,000,000						6,000,000
Warehouse Facilities | Originations | Notes payable to banks | $40 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.30%
Warehouse Facilities | Originations | Notes payable to banks | $1,200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 1,200,000,000		800,000,000
MSR Facilities | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	266,000,000						160,000,000
Collateral Pledged	1,075,000,000						1,359,000,000
MSR Facilities | Originations | Notes payable to banks | $450 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	450,000,000
Debt outstanding, gross	0						150,000,000
Collateral Pledged	$ 0						945,000,000
MSR Facilities | Originations | Notes payable to banks | $450 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	5.10%
MSR Facilities | Originations | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000		$ 400,000,000
Debt outstanding, gross	0						0
Collateral Pledged	$ 187,000,000						200,000,000
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	$ 149,000,000						130,000,000
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						84,000,000
MSR Facilities | Originations | Notes payable to banks | $50 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.80%
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	144,000,000						0
Collateral Pledged	$ 196,000,000						0
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 | $500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 260,000,000
Debt outstanding, gross	256,000,000						0
Collateral Pledged	$ 659,000,000						0
MSR Financing, Internally Allocated | Originations | Notes payable to banks | $500 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.90%
Advance, Warehouse and MSR Facilities | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 4,863,000,000						4,998,000,000
Collateral Pledged	6,004,000,000						6,646,000,000
Unamortized debt issuance costs	(12,000,000)						(1,000,000)
Debt Outstanding	$ 4,851,000,000						$ 4,997,000,000