Financing Arrangements - Additional Information (Detail) - DebtFinancing	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Number of debt financing arrangements in place	0
Number of debt financing arrangements in place other than second lien notes		0

Number of debt financing arrangements other than second lien notes.

No definition available.

Name:	wmih_NumberOfDebtFinancingArrangementsOtherThanSecondLienNotes
Namespace Prefix:	wmih_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant