Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2018	Mar. 31, 2018	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Deferred tax assets, NOL		$ 998,000,000	$ 1,334,000,000
Unrecognized tax benefits	$ 17,000,000	0	0	$ 0		$ 0
Unrecognized tax benefits, uncertain tax positions	19,000,000
Interest and penalties expense	$ 2,000,000
Unrecognized tax benefits, net effect					$ 6,000,000
WMIH Corp
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, valuation allowance		285,000,000
Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, valuation allowance		9,000,000
Operating loss carryforwards		$ 4,700,000,000	$ 6,300,000,000