Carrying amount of Securities Sold

No definition available.

Name:	asb_CarryingamountofSecuritiesSold
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Debt Securities, AFS, Principal Sold

+ References

No definition available.

+ Details

Name:	asb_DebtSecuritiesAFSPrincipalSold
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Investment securities.

+ References

No definition available.

+ Details

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

- Definition

Taxable Equivalent Yield

+ References

No definition available.

+ Details

Name:	asb_TaxableEquivalentYield
Namespace Prefix:	asb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Visa Restricted Stock Donated

+ References

No definition available.

+ Details

Name:	asb_VisaRestrictedStockDonated
Namespace Prefix:	asb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Visa Restricted Stock Owned

+ References

No definition available.

+ Details

Name:	asb_VisaRestrictedStockOwned
Namespace Prefix:	asb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
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), with interest rate reset through auction process, sold at par value.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableforsaleSecuritiesSoldAtPar
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27405-111563

+ Details

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

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

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

- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117539-209714

+ Details

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

- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

+ Details

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

- Definition

Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

+ Details

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

- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=asb_BankMutualMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=asb_SecuritiesSoldMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=asb_SecuritiesReinvestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=asb_GNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Investment Securities (Details Textual) - USD ($) $ in Millions		3 Months Ended			6 Months Ended	9 Months Ended
	Feb. 01, 2018	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Debt Securities, Available-for-sale, Sold at Par Value				$ 108
Investment Securities (Textuals) [Abstract]
Transfer of securities from held to maturity to available for sale		$ 692
Debt Securities, AFS, Principal Sold		157
Debt Securities, Available-for-sale, Gain (Loss)		$ 3
Carrying amount of Securities Sold						$ 1,200
Visa Restricted Stock Donated			42,039
Visa Restricted Stock Owned		77,000
Debt Securities, Available-for-sale, Sold at Par Value				$ 108
Pledged Financial Instruments, Not Separately Reported, Securities		$ 3,000				3,000	$ 3,000
Federal Home Loan Bank Stock		129				129	173
Federal Reserve Bank Stock		78				78	77
Equity securities with readily determinable fair values, Fair Value		2				2	2
Equity Securities without Readily Determinable Fair Value, Amount		$ 13				$ 13	$ 0
Bank Mutual
Business Acquisition [Line Items]
Debt Securities, Available-for-sale, Sold at Par Value	$ 453
Investment Securities (Textuals) [Abstract]
Debt Securities, Available-for-sale, Sold at Par Value	$ 453
Securities Sold [Member]
Business Acquisition [Line Items]
Taxable Equivalent Yield				3.08%
Securities Reinvest [Member]
Business Acquisition [Line Items]
Taxable Equivalent Yield				3.51%
GNMA [Member] \| Commercial mortgage-related securities
Business Acquisition [Line Items]
Debt Securities, Available-for-sale, Sold at Par Value					$ 40
Investment Securities (Textuals) [Abstract]
Debt Securities, Available-for-sale, Sold at Par Value					$ 40