Acquisitions - Acquisition of Nationstar Mortgage Holdings Inc (Details)				3 Months Ended			6 Months Ended
	Aug. 01, 2018 USD ($)	Jul. 31, 2018 USD ($) $ / shares shares	Jul. 13, 2018 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jul. 12, 2018 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 120,000,000			$ 120,000,000		$ 23,000,000
Reduction in payables and accrued liabilities							(31,000,000)	$ (9,000,000)
Goodwill adjustment							55,000,000
Nationstar Mortgage Holdings Inc.
Business Acquisition [Line Items]
Cash consideration	$ 1,226,000,000
Estimated consideration	1,777,000,000
Stock consideration	551,000,000
Goodwill	$ 65,000,000			65,000,000			65,000,000		$ 10,000,000
Reduction in reverse mortgage interests					$ 24,000,000
Reduction in reverse mortgage servicing rights					6,000,000
Increase in mortgage servicing liabilities					37,000,000
Reduction in payables and accrued liabilities					12,000,000
Goodwill adjustment					55,000,000		55,000,000
Accounting adjustments					8,000,000
WMIH Corp And Wand Merger Corporation
Business Acquisition [Line Items]
Right to receive in shares (in dollars per share) | $ / shares		$ 18
Right to receive in shares (shares) | shares		12.7793
Stock split conversion		0.0833
Acquisition costs		$ 27,000,000
Acquisition costs, incurred				$ 0		$ 1,000,000	$ 1,000,000	4,000,000
8.125% Due July 2023
Business Acquisition [Line Items]
Debt issued			$ 950,000,000
Interest rate			8.125%
9.125% Due July 2026
Business Acquisition [Line Items]
Debt issued			$ 750,000,000
Interest rate			9.125%
Service related, net revenue | Nationstar Mortgage Holdings Inc.
Business Acquisition [Line Items]
Accounting adjustments					7,000,000
Interest income | Nationstar Mortgage Holdings Inc.
Business Acquisition [Line Items]
Accounting adjustments					$ 1,000,000
WMIH Corp | WMIH Corp And Wand Merger Corporation
Business Acquisition [Line Items]
Acquisition costs										$ 92,000,000
Acquisition costs, incurred						$ 3,000,000		$ 7,000,000
Debt issuance costs										38,000,000
WMIH Corp | KCM | WMIH Corp And Wand Merger Corporation
Business Acquisition [Line Items]
Acquisition costs										7,000,000
Payment for conversion fee			$ 8,000,000
WMIH Corp | KKR Capital Markets LLC | WMIH Corp And Wand Merger Corporation
Business Acquisition [Line Items]
Acquisition costs										$ 25,000,000