Indebtedness - Notes Payable Summary (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	May 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt Outstanding	$ 475,000,000				$ 422,000,000
Originations | Mortgage servicing rights
Debt Instrument [Line Items]
Capacity Amount	150,000,000
Originations | Mortgage loans held for sale
Debt Instrument [Line Items]
Collateral Pledged	3,016,000,000				3,931,000,000
Debt Outstanding	2,963,000,000				3,826,000,000
Originations | Reverse mortgage interests
Debt Instrument [Line Items]
Collateral Pledged	741,000,000				691,000,000
Debt Outstanding	624,000,000				590,000,000
Originations | MSR
Debt Instrument [Line Items]
Collateral Pledged	1,008,000,000				1,359,000,000
Debt Outstanding	445,000,000				160,000,000
Advance Facilities | Servicing
Debt Instrument [Line Items]
Debt outstanding, gross	480,000,000				422,000,000
Collateral Pledged	599,000,000				665,000,000
Unamortized debt issuance costs	(5,000,000)				0
Debt Outstanding	475,000,000				422,000,000
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	193,000,000				37,000,000
Collateral Pledged	$ 220,000,000				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	211,000,000				224,000,000
Collateral Pledged	$ 273,000,000				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 | $200 advance facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	76,000,000				63,000,000
Collateral Pledged	$ 106,000,000				125,000,000
Advance Facilities | Servicing | Notes payable to banks | $200 advance facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations
Debt Instrument [Line Items]
Debt outstanding, gross	$ 3,587,000,000				4,416,000,000
Collateral Pledged	3,757,000,000				4,622,000,000
Warehouse Facilities | Originations | $800 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	800,000,000
Warehouse Facilities | Originations | Notes payable to banks | $1,500 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	1,500,000,000
Debt outstanding, gross	669,000,000				759,000,000
Collateral Pledged	$ 637,000,000				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	568,000,000				683,000,000
Collateral Pledged	$ 606,000,000				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 | $800 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 800,000,000
Debt outstanding, gross	642,000,000				589,000,000
Collateral Pledged	$ 700,000,000				656,000,000
Warehouse Facilities | Originations | Notes payable to banks | $800 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	2.10%
Warehouse Facilities | Originations | Notes payable to banks | $800 warehouse facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on rate	3.80%
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 750,000,000
Debt outstanding, gross	572,000,000				411,000,000
Collateral Pledged	$ 583,000,000				425,000,000
Warehouse Facilities | Originations | Notes payable to banks | $750 warehouse facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on rate	1.40%
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 | $700 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 700,000,000
Debt outstanding, gross	624,000,000				469,000,000
Collateral Pledged	$ 644,000,000				488,000,000
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	233,000,000				174,000,000
Collateral Pledged	$ 278,000,000				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	$ 1,000,000				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 | $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	175,000,000				136,000,000
Collateral Pledged	$ 175,000,000				136,000,000
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	1.40%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	50,000,000				54,000,000
Collateral Pledged	$ 74,000,000				78,000,000
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.50%
Warehouse Facilities | Originations | Notes payable to banks | $200 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Debt outstanding, gross	19,000,000				27,000,000
Collateral Pledged	$ 19,000,000				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	31,000,000				11,000,000
Collateral Pledged	$ 36,000,000				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	4,000,000				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%
MSR Facility | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 445,000,000				160,000,000
Collateral Pledged	1,008,000,000				1,359,000,000
MSR Facility | Originations | Notes payable to banks | $450 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	450,000,000	$ 450,000,000		$ 400,000,000
Debt outstanding, gross	300,000,000				150,000,000
Collateral Pledged	$ 628,000,000				945,000,000
MSR Facility | Originations | Notes payable to banks | $450 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	5.10%
MSR Facility | Originations | Notes payable to banks | $400 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 400,000,000
Debt outstanding, gross	75,000,000				0
Collateral Pledged	$ 176,000,000				200,000,000
MSR Facility | Originations | Notes payable to banks | $400 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.30%
MSR Facility | Originations | Notes payable to banks | $150 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 150,000,000
Debt outstanding, gross	40,000,000				0
Collateral Pledged	$ 117,000,000				130,000,000
MSR Facility | Originations | Notes payable to banks | $150 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	3.80%
MSR Facility | Originations | Notes payable to banks | $50 warehouse facility
Debt Instrument [Line Items]
Capacity Amount	$ 50,000,000
Debt outstanding, gross	30,000,000				10,000,000
Collateral Pledged	$ 87,000,000				84,000,000
MSR Facility | Originations | Notes payable to banks | $50 warehouse facility | LIBOR
Debt Instrument [Line Items]
Basis spread on rate	2.80%
Warehouse and MSR facilities | Originations | Notes payable to banks
Debt Instrument [Line Items]
Debt outstanding, gross	$ 4,032,000,000				4,576,000,000
Collateral Pledged	4,765,000,000				5,981,000,000
Unamortized debt issuance costs	(1,000,000)				(1,000,000)
Debt Outstanding	$ 4,031,000,000				$ 4,575,000,000