Investment Securities AFS Securities Amortized Cost and Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investment securities available for sale:
Investment securities available for sale, amortized cost	$ 5,368,259	$ 5,270,576
Investment securities available for sale, gross unrealized gains	85,085	88,043
Investment securities available for sale, gross unrealized losses	(56,532)	(108,034)
Investment securities available for sale, at fair value	5,396,812us-gaap_AvailableForSaleSecurities	5,250,585us-gaap_AvailableForSaleSecurities
US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	999	1,001
Investment securities available for sale, gross unrealized gains	0	1
Investment securities available for sale, gross unrealized losses	(1)	0
Investment securities available for sale, at fair value	998	1,002
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	560,839	653,758
Investment securities available for sale, gross unrealized gains	21,869	23,855
Investment securities available for sale, gross unrealized losses	(29)	(1,533)
Investment securities available for sale, at fair value	582,679	676,080
Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	3,700,103	3,855,467
Investment securities available for sale, gross unrealized gains	61,236	61,542
Investment securities available for sale, gross unrealized losses	(30,550)	(78,579)
Investment securities available for sale, at fair value	3,730,789	3,838,430
Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	2,297	3,035
Investment securities available for sale, gross unrealized gains	7	16
Investment securities available for sale, gross unrealized losses	(10)	37
Investment securities available for sale, at fair value	2,294	3,014
GSE Commercial Mortgage-Related Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	1,097,913	673,555
Investment securities available for sale, gross unrealized gains	1,922	1,764
Investment securities available for sale, gross unrealized losses	(25,942)	(27,842)
Investment securities available for sale, at fair value	1,073,893	647,477
Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	0	23,049
Investment securities available for sale, gross unrealized gains	0	10
Investment securities available for sale, gross unrealized losses	0	0
Investment securities available for sale, at fair value	0	23,059
Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	6,108	60,711
Investment securities available for sale, gross unrealized gains	51	855
Investment securities available for sale, gross unrealized losses	0	(43)
Investment securities available for sale, at fair value	$ 6,159	$ 61,523

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

No definition available.

+ Details

Name:	asb_Availableforsalesecuritiesaccumulatedgrossunrealizedgainbeforetax
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

Name:	asb_Availableforsalesecuritiesaccumulatedgrossunrealizedlossbeforetax
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

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

- Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=asb_OtherDebtAndOtherEquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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