Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2018	Mar. 31, 2018
Tax Credit Carryforward [Line Items]
Valuation allowance	$ 295
Tax benefit remeasurement of deferred tax assets and liabilities	3
Unrecognized tax benefits, uncertain tax positions		$ 19
Interest and penalties expense		$ 2
Unrecognized tax benefits, net effect				$ 6
WMIH Corp
Tax Credit Carryforward [Line Items]
Valuation allowance			$ 1,300
Federal Net Operating Loss Carryforwards And Other Deferred Tax Assets
Tax Credit Carryforward [Line Items]
Release of valuation allowance	$ 990