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Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
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Significant Accounting Policies [Line Items] |  |
Premium deficiency reserves | $ 15.8 | $ 3.1

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- Definition Premium deficiency reserves. + References No definition available. + Details
Name: | wmih_PremiumDeficiencyReserves
Namespace Prefix: | wmih_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | wmih_SignificantAccountingPoliciesLineItems
Namespace Prefix: | wmih_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration