Indebtedness - Notes Payable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (10,000,000)	$ (68,000,000)
Outstanding debt	422,000,000	595,000,000
Warehouse and MSR Facilities
Debt Instrument [Line Items]
Unamortized debt issuance costs	(1,000,000)	(1,000,000)
Outstanding debt	4,575,000,000	2,349,000,000
Servicing | Advance facilities
Debt Instrument [Line Items]
Outstanding	422,000,000	595,000,000
Collateral Pledged	665,000,000	777,000,000
Unamortized debt issuance costs	0	0
Outstanding debt	422,000,000	595,000,000
Originations | Warehouse facilities
Debt Instrument [Line Items]
Outstanding	4,416,000,000	2,250,000,000
Collateral Pledged	4,622,000,000	2,466,000,000
Originations | MSR Facility
Debt Instrument [Line Items]
Outstanding	160,000,000	100,000,000
Collateral Pledged	1,359,000,000	1,686,000,000
Originations | Warehouse and MSR Facilities
Debt Instrument [Line Items]
Outstanding	4,576,000,000	2,350,000,000
Collateral Pledged	5,981,000,000	4,152,000,000
Originations | $800 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	800,000,000
Mortgage Servicing Rights | Originations
Debt Instrument [Line Items]
Capacity Amount	150,000,000
Mortgage loans held for sale and mortgage loans held for investment | Originations
Debt Instrument [Line Items]
Collateral Pledged	3,931,000,000	1,628,000,000
Outstanding debt	3,826,000,000	1,528,000,000
Reverse mortgage interests | Originations
Debt Instrument [Line Items]
Collateral Pledged	691,000,000	838,000,000
Outstanding debt	590,000,000	722,000,000
MSR | Originations
Debt Instrument [Line Items]
Collateral Pledged	1,359,000,000	1,686,000,000
Outstanding debt	160,000,000	100,000,000
Loans Payable | Servicing | $325 advance facility | Advance facilities
Debt Instrument [Line Items]
Capacity Amount	325,000,000
Outstanding	224,000,000	209,000,000
Collateral Pledged	285,000,000	284,000,000
Loans Payable | Servicing | $250 advance facility | Advance facilities
Debt Instrument [Line Items]
Capacity Amount	250,000,000
Outstanding	98,000,000	218,000,000
Collateral Pledged	167,000,000	255,000,000
Loans Payable | Servicing | $125 advance facility | Advance facilities
Debt Instrument [Line Items]
Capacity Amount	125,000,000
Outstanding	37,000,000	78,000,000
Collateral Pledged	$ 88,000,000	89,000,000
Loans Payable | Minimum | LIBOR | Servicing | $325 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Loans Payable | Minimum | LIBOR | Servicing | $250 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Loans Payable | Minimum | CPRATE | Servicing | $125 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Loans Payable | Maximum | LIBOR | Servicing | $325 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	6.50%
Loans Payable | Maximum | LIBOR | Servicing | $250 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	2.60%
Loans Payable | Maximum | CPRATE | Servicing | $125 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	7.40%
Notes Payable to Banks | Servicing | $200 advance facility | Advance facilities
Debt Instrument [Line Items]
Capacity Amount	$ 200,000,000
Outstanding	63,000,000	90,000,000
Collateral Pledged	125,000,000	149,000,000
Notes Payable to Banks | Originations | $1,500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	1,500,000,000
Outstanding	759,000,000	0
Collateral Pledged	733,000,000	0
Notes Payable to Banks | Originations | $1,200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	1,200,000,000
Outstanding	683,000,000	560,000,000
Collateral Pledged	724,000,000	622,000,000
Notes Payable to Banks | Originations | $1,000 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	1,000,000,000
Outstanding	762,000,000	137,000,000
Collateral Pledged	783,000,000	140,000,000
Notes Payable to Banks | Originations | $800 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	800,000,000
Outstanding	589,000,000	464,000,000
Collateral Pledged	656,000,000	514,000,000
Notes Payable to Banks | Originations | $750 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	750,000,000
Outstanding	411,000,000	119,000,000
Collateral Pledged	425,000,000	122,000,000
Notes Payable to Banks | Originations | $700 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	700,000,000
Outstanding	469,000,000	220,000,000
Collateral Pledged	488,000,000	248,000,000
Notes Payable to Banks | Originations | $600 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	600,000,000
Outstanding	174,000,000	151,000,000
Collateral Pledged	202,000,000	168,000,000
Notes Payable to Banks | Originations | $500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	500,000,000
Outstanding	336,000,000	187,000,000
Collateral Pledged	349,000,000	200,000,000
Notes Payable to Banks | Originations | $500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	500,000,000
Outstanding	0	290,000,000
Collateral Pledged	0	299,000,000
Notes Payable to Banks | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Outstanding	136,000,000	0
Collateral Pledged	136,000,000	0
Notes Payable to Banks | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Outstanding	27,000,000	18,000,000
Collateral Pledged	27,000,000	19,000,000
Notes Payable to Banks | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	200,000,000
Outstanding	54,000,000	103,000,000
Collateral Pledged	78,000,000	132,000,000
Notes Payable to Banks | Originations | $200 warehouse facility | 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	11,000,000	0
Collateral Pledged	15,000,000	0
Notes Payable to Banks | Originations | $40 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	40,000,000
Outstanding	5,000,000	0
Collateral Pledged	6,000,000	0
Notes Payable to Banks | Originations | $40 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Capacity Amount	40,000,000
Outstanding	0	1,000,000
Collateral Pledged	0	2,000,000
Notes Payable to Banks | Originations | $400 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Capacity Amount	400,000,000
Outstanding	150,000,000	100,000,000
Collateral Pledged	945,000,000	928,000,000
Notes Payable to Banks | Originations | $400 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Capacity Amount	400,000,000
Outstanding	0	0
Collateral Pledged	200,000,000	226,000,000
Notes Payable to Banks | Originations | $150 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Capacity Amount	150,000,000
Outstanding	0	0
Collateral Pledged	130,000,000	430,000,000
Notes Payable to Banks | Originations | $50 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Capacity Amount	50,000,000
Outstanding	10,000,000	0
Collateral Pledged	$ 84,000,000	$ 102,000,000
Notes Payable to Banks | LIBOR | Servicing | $200 advance facility | Advance facilities
Debt Instrument [Line Items]
Interest Rate	2.50%
Notes Payable to Banks | LIBOR | Originations | $1,500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.00%
Notes Payable to Banks | LIBOR | Originations | $600 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.30%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.40%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.20%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.00%
Notes Payable to Banks | LIBOR | Originations | $200 warehouse facility | 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 | $40 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	3.00%
Notes Payable to Banks | LIBOR | Originations | $400 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Interest Rate	2.30%
Notes Payable to Banks | LIBOR | Originations | $150 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Interest Rate	2.80%
Notes Payable to Banks | LIBOR | Originations | $50 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Interest Rate	4.50%
Notes Payable to Banks | Minimum | LIBOR | Originations | $1,200 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Notes Payable to Banks | Minimum | LIBOR | Originations | $1,000 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.40%
Notes Payable to Banks | Minimum | LIBOR | Originations | $800 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Notes Payable to Banks | Minimum | LIBOR | Originations | $750 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.40%
Notes Payable to Banks | Minimum | LIBOR | Originations | $700 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.30%
Notes Payable to Banks | Minimum | LIBOR | Originations | $500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	1.50%
Notes Payable to Banks | Minimum | LIBOR | Originations | $500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.00%
Notes Payable to Banks | Minimum | LIBOR | Originations | $50 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.00%
Notes Payable to Banks | Minimum | LIBOR | Originations | $400 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Interest Rate	3.50%
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 | $1,000 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.30%
Notes Payable to Banks | Maximum | LIBOR | Originations | $800 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.90%
Notes Payable to Banks | Maximum | LIBOR | Originations | $750 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.80%
Notes Payable to Banks | Maximum | LIBOR | Originations | $700 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	2.20%
Notes Payable to Banks | Maximum | LIBOR | Originations | $500 warehouse facility | Warehouse facilities
Debt Instrument [Line Items]
Interest Rate	3.00%
Notes Payable to Banks | Maximum | LIBOR | Originations | $500 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	6.00%
Notes Payable to Banks | Maximum | LIBOR | Originations | $400 warehouse facility | MSR Facility
Debt Instrument [Line Items]
Interest Rate	6.10%