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Retirement Plans (Details Textuals) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Retirements Plans [Line Items]      
Retirement eligible age for participation 55asb_DefinedBenefitPostretirementPlanHealthCareAccessEligibilityTerms1    
Years eligble of service for participation 5asb_Definedbenefitpostretirementplanhealthcareaccesseligibilityterms2    
Expected long-term rate of return on plan assets 7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets 7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets  
Actual return on plan assets percentage 5.89%asb_DefinedBenefitPlanActualReturnOnPlanAssetsPercentage 18.54%asb_DefinedBenefitPlanActualReturnOnPlanAssetsPercentage  
Contribution made by the Corporation to pension plan $ 21,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer $ 28,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer  
Total expense related to 401(k) 10,000,000us-gaap_DefinedContributionPlanCostRecognized 11,000,000us-gaap_DefinedContributionPlanCostRecognized 10,000,000us-gaap_DefinedContributionPlanCostRecognized
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation 177.00%asb_Fairvalueofplanassetsasapercentageofnetbenefitobligation 182.00%asb_Fairvalueofplanassetsasapercentageofnetbenefitobligation  
Acturial Losses [Member]      
Retirements Plans [Line Items]      
Amounts to be amortized from AOCI next fiscal year 2,100,000us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ asb_ComponentsOfNetPeriodicBenefitCostAxis
= asb_ActurialLossesMember
   
Equity Securities [Member]      
Retirements Plans [Line Items]      
Plan asset allocation minimum percentage 50.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMinimum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_EquitySecuritiesMember
   
Plan asset allocation maximum percentage 70.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMaximum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_EquitySecuritiesMember
   
Debt Securities [Member]      
Retirements Plans [Line Items]      
Plan asset allocation minimum percentage 30.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMinimum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_DebtSecuritiesMember
   
Plan asset allocation maximum percentage 50.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMaximum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_DebtSecuritiesMember
   
CashAndCashEquivalentsMember      
Retirements Plans [Line Items]      
Plan asset allocation minimum percentage 0.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMinimum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_CashAndCashEquivalentsMember
   
Plan asset allocation maximum percentage 5.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMaximum
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_CashAndCashEquivalentsMember
   
CashAndCashEquivalentsMember | Prior Service Cost [Member]      
Retirements Plans [Line Items]      
Amounts to be amortized from AOCI next fiscal year $ 100,000us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ asb_AssetAllocationPorfolioSegmentsAxis
= us-gaap_CashAndCashEquivalentsMember
/ asb_ComponentsOfNetPeriodicBenefitCostAxis
= asb_PriorServiceCostMember
   
Alternative Securities [Member]      
Retirements Plans [Line Items]      
Plan asset allocation minimum percentage 0.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMinimum
/ asb_AssetAllocationPorfolioSegmentsAxis
= asb_AlternativeSecuritiesMember
   
Plan asset allocation maximum percentage 15.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMaximum
/ asb_AssetAllocationPorfolioSegmentsAxis
= asb_AlternativeSecuritiesMember
   
Pre-65 Health Care Trend Rate [Member]      
Retirements Plans [Line Items]      
Health care trend rate assumption 9.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ asb_HealthCareTrendRateByAgeAxis
= asb_Pre65HealthCareTrendRateMember
   
Change in assumption .5% lower in each succeeding year    
Ultimate future rate 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ asb_HealthCareTrendRateByAgeAxis
= asb_Pre65HealthCareTrendRateMember
   
Post-65 Health Care Trend [Member]      
Retirements Plans [Line Items]      
Health care trend rate assumption 8.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ asb_HealthCareTrendRateByAgeAxis
= asb_Post65HealthCareTrendMember
   
Change in assumption .5% lower in each succeeding year    
Ultimate future rate 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ asb_HealthCareTrendRateByAgeAxis
= asb_Post65HealthCareTrendMember