Loans, Modifications (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified, Weighted Average Term, Range, From	308 months	258 months
Financing Receivable, Modified, Weighted Average Term, Range, To	409 months	399 months
Interest Rate Below Market Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 857	$ 1,063
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	(5.00%)	(8.00%)
Extended Maturity [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified, Weighted Average Term Increase from Modification	101 months	141 months
Extended Maturity and Interest Rate Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 2,384	$ 1,704
Commercial and Industrial Sector \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 153	$ 176
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	(22.00%)	(25.00%)
Residential Mortgage [Member] \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	1.00%	1.00%
Residential Mortgage [Member] \| Extended Maturity [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 510	$ 0
Financing Receivable, Modified, Weighted Average Term Increase from Modification	102 months	145 months
Residential Mortgage [Member] \| Extended Maturity and Interest Rate Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 2,330	$ 1,644
Home Equity Line of Credit [Member] \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	(3.00%)	(4.00%)
Home Equity Line of Credit [Member] \| Extended Maturity [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified, Weighted Average Term Increase from Modification	60 months	60 months
Home Equity Line of Credit [Member] \| Extended Maturity and Interest Rate Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 54	$ 61
Other Consumer [Member] \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Modified [Line Items]
Financing Receivable, Modified in Period, Amount	$ 704	$ 887
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	(21.00%)	(21.00%)

Financing Receivable, Modified, Weighted Average Term, Range, From

No definition available.

Name:	asb_FinancingReceivableModifiedWeightedAverageTermRangeFrom
Namespace Prefix:	asb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Modified, Weighted Average Term, Range, To

+ References

No definition available.

+ Details

Name:	asb_FinancingReceivableModifiedWeightedAverageTermRangeTo
Namespace Prefix:	asb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-34

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost of financing receivable modified during period for debtor experiencing financial difficulty.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of decrease in weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateDecreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_InterestRateBelowMarketReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityAndInterestRateReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=asb_OtherConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: