Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2022	Dec. 31, 2021
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 2,852,501	$ 4,338,671
Debt Securities, Available-for-sale, Unrealized Gain	1,234	28,850
Debt Securities, Available-for-sale, Unrealized Loss	(176,224)	(35,506)
Debt Securities, Available-for-sale	2,677,511	4,332,015
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	3,945,269	2,239,003
Held-to-maturity, Gross Unrealized Gains	68,474	118,471
Held-to-maturity, Gross Unrealized Loss	(479,551)	(8,809)
Held-to-maturity, Fair Value	3,534,192	2,348,664
US Treasury Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	124,365	124,291
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(11,256)	(1,334)
Debt Securities, Available-for-sale	113,109	122,957
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	998	1,000
Held-to-maturity, Gross Unrealized Gains	0	1
Held-to-maturity, Gross Unrealized Loss	(44)	0
Held-to-maturity, Fair Value	955	1,001
Agency Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	15,000	15,000
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(1,041)	(103)
Debt Securities, Available-for-sale	13,959	14,897
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	361,712	381,517
Debt Securities, Available-for-sale, Unrealized Gain	648	18,940
Debt Securities, Available-for-sale, Unrealized Loss	(3,518)	0
Debt Securities, Available-for-sale	358,842	400,457
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	1,717,627	1,628,759
Held-to-maturity, Gross Unrealized Gains	4,002	113,179
Held-to-maturity, Gross Unrealized Loss	(161,116)	(1,951)
Held-to-maturity, Fair Value	1,560,514	1,739,988
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	0	332,028
Debt Securities, Available-for-sale, Unrealized Gain		31
Debt Securities, Available-for-sale, Unrealized Loss		(2,335)
Debt Securities, Available-for-sale	0	329,724
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	375,638
Held-to-maturity, Gross Unrealized Gains	12,693
Held-to-maturity, Gross Unrealized Loss	(54,490)
Held-to-maturity, Fair Value	333,841
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	168,357	177,974
Debt Securities, Available-for-sale, Unrealized Gain	0	475
Debt Securities, Available-for-sale, Unrealized Loss	(7,092)	(1,123)
Debt Securities, Available-for-sale	161,264	177,325
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	0
Held-to-maturity, Fair Value	0
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,287	6,594
Debt Securities, Available-for-sale, Unrealized Gain	40	39
Debt Securities, Available-for-sale, Unrealized Loss	(45)	(54)
Debt Securities, Available-for-sale	5,281	6,580
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	0
Held-to-maturity, Fair Value	0
Other Debt securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,000	3,000
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(71)	(6)
Debt Securities, Available-for-sale	2,929	2,994
FNMA/FHLMC \| Residential Related Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,959,641	2,709,399
Debt Securities, Available-for-sale, Unrealized Gain	547	3,729
Debt Securities, Available-for-sale, Unrealized Loss	(148,585)	(21,249)
Debt Securities, Available-for-sale	1,811,603	2,691,879
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	967,421	34,347
Held-to-maturity, Gross Unrealized Gains	34,108	1,792
Held-to-maturity, Gross Unrealized Loss	(125,444)	0
Held-to-maturity, Fair Value	876,085	36,139
FNMA/FHLMC \| Commercial mortgage-related securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	19,207	357,240
Debt Securities, Available-for-sale, Unrealized Gain	0	2,686
Debt Securities, Available-for-sale, Unrealized Loss	(601)	(9,302)
Debt Securities, Available-for-sale	18,606	350,623
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	762,086	425,937
Held-to-maturity, Gross Unrealized Gains	16,835	122
Held-to-maturity, Gross Unrealized Loss	(131,851)	(6,659)
Held-to-maturity, Fair Value	647,070	419,400
Government National Mortgage Association (GNMA) [Member] \| Residential Related Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	87,779	66,189
Debt Securities, Available-for-sale, Unrealized Gain	0	1,591
Debt Securities, Available-for-sale, Unrealized Loss	(1,542)	0
Debt Securities, Available-for-sale	86,238	67,780
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	42,248	48,053
Held-to-maturity, Gross Unrealized Gains	37	1,578
Held-to-maturity, Gross Unrealized Loss	(1,637)	0
Held-to-maturity, Fair Value	40,649	49,631
Government National Mortgage Association (GNMA) [Member] \| Commercial mortgage-related securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	108,153	165,439
Debt Securities, Available-for-sale, Unrealized Gain	0	1,360
Debt Securities, Available-for-sale, Unrealized Loss	(2,473)	0
Debt Securities, Available-for-sale	105,680	166,799
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	79,250	100,907
Held-to-maturity, Gross Unrealized Gains	799	1,799
Held-to-maturity, Gross Unrealized Loss	(4,970)	(200)
Held-to-maturity, Fair Value	$ 75,079	$ 102,506

[Line Items] for Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Table]

No definition available.

Name:	asb_ScheduleofAvailableforsaleandHeldtomaturitySecuritiesTableLineItems
Namespace Prefix:	asb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesGrossUnrealizedGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563

+ Details

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=SL120269820-111563

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_AgencySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_FederalFamilyEducationLoanProgramFfelpGuaranteedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=asb_FNMAFHLMCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=us-gaap_GovernmentNationalMortgageAssociationGnmaInsuredLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: