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Retirement Plans (Details Textuals) (Details) $ in Millions | Jun. 30, 2018 USD ($)
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Other Pension Plan [Member] |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
OneTimePensionPlanContribution | $ 31

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- Definition One Time Pension Plan Contribution + References No definition available. + Details
Name: | asb_OneTimePensionPlanContribution
Namespace Prefix: | asb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |