Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Income Statement Data Abstract
Net interest income	$ 680,967us-gaap_InterestIncomeExpenseNet	$ 645,543us-gaap_InterestIncomeExpenseNet	$ 625,992us-gaap_InterestIncomeExpenseNet
Noninterest income	290,319us-gaap_NoninterestIncome	313,099us-gaap_NoninterestIncome	313,290us-gaap_NoninterestIncome
Total revenue	971,286us-gaap_Revenues	958,642us-gaap_Revenues	939,282us-gaap_Revenues
Provision for credit losses	16,000	10,100	10,100
Noninterest expense	679,241us-gaap_NoninterestExpense	680,649us-gaap_NoninterestExpense	674,723us-gaap_NoninterestExpense
Income before income taxes	276,045	267,893	254,459
Income tax expense	85,536us-gaap_IncomeTaxExpenseBenefit	79,201us-gaap_IncomeTaxExpenseBenefit	75,486us-gaap_IncomeTaxExpenseBenefit
Net income	190,509us-gaap_NetIncomeLoss	188,692us-gaap_NetIncomeLoss	178,973us-gaap_NetIncomeLoss
Return on average allocated capital	9.90%asb_Returnonaverageallocatedcapital	9.80%asb_Returnonaverageallocatedcapital	9.50%asb_Returnonaverageallocatedcapital
Segment Balance Sheet Data
Average earning assets	22,760,128asb_AverageEarningAssets	20,980,128asb_AverageEarningAssets	19,613,777asb_AverageEarningAssets
Average loans	16,838,994	15,663,145	14,741,785
Average deposits	17,647,084asb_AverageDeposits	17,438,195asb_AverageDeposits	15,582,369asb_AverageDeposits
Average allocated capital	1,870,609asb_AverageAllocatedCapital	1,878,371asb_AverageAllocatedCapital	1,838,424asb_AverageAllocatedCapital
Commercial Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	284,177	299,405	271,902
Noninterest income	46,953	43,944	37,853
Total revenue	331,130	343,349	309,755
Provision for credit losses	44,819	51,217	44,653
Noninterest expense	141,302	140,508	139,009
Income before income taxes	145,009	151,624	126,093
Income tax expense	48,133	53,068	44,133
Net income	96,876	98,556	81,960
Return on average allocated capital	13.20%	13.40%	11.90%
Segment Balance Sheet Data
Average earning assets	8,600,750	7,962,250	7,066,657
Average loans	8,588,847	7,952,436	7,060,181
Average deposits	4,861,001	5,056,710	4,196,607
Average allocated capital	734,130	733,862	688,361
Community, Consumer, and Business [Member]
Segment Income Statement Data Abstract
Net interest income	319,743	335,988	320,499
Noninterest income	223,639	252,140	256,292
Total revenue	543,382	588,128	576,791
Provision for credit losses	25,972	24,202	27,130
Noninterest expense	470,358	475,261	490,129
Income before income taxes	47,052	88,665	59,532
Income tax expense	16,468	31,033	20,836
Net income	30,584	57,632	38,696
Return on average allocated capital	5.30%	9.90%	6.40%
Segment Balance Sheet Data
Average earning assets	8,167,003	7,706,896	7,656,611
Average loans	8,167,003	7,706,896	7,656,611
Average deposits	10,348,689	10,098,159	9,857,938
Average allocated capital	578,101	580,019	605,707
Risk Management and Shared Serivies [Member]
Segment Income Statement Data Abstract
Net interest income	77,047	10,150	33,591
Noninterest income	19,727	17,015	19,145
Total revenue	96,774	27,165	52,736
Provision for credit losses	(54,791)	(65,319)	(61,683)
Noninterest expense	67,581	64,880	45,585
Income before income taxes	83,984	27,604	68,834
Income tax expense	20,935	(4,900)	10,517
Net income	63,049	32,504	58,317
Return on average allocated capital	10.40%	4.80%	9.80%
Segment Balance Sheet Data
Average earning assets	5,992,375	5,310,982	4,890,509
Average loans	83,144	3,813	24,993
Average deposits	2,437,394	2,283,326	1,527,824
Average allocated capital	$ 558,378	$ 564,490	$ 544,356

Average allocated tier 1 common equity

No definition available.

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

- Definition

Average deposits

+ References

No definition available.

+ Details

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

- Definition

Average earning assets

+ References

No definition available.

+ Details

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

- Definition

Return on average allocated tier 1 common equity

+ References

No definition available.

+ Details

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

- Details

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

- Definition

This is the result of the average balance during the period of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=13989330&loc=d3e107314-111719

+ Details

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

- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

+ Details

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

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Income Tax Expense (or Benefit)

-URI http://asc.fasb.org/extlink&oid=6515339

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319

+ Details

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

- Definition

The net amount of operating interest income (expense).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.10)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 10

-Article 9

+ Details

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

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 20

-Article 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.19)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.18)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.22)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e565-108580

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 19

-Article 5

+ Details

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

- Definition

Total aggregate amount of all noninterest expense.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.14)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 14

-Article 9

+ Details

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

- Definition

The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 13

-Article 9

+ Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.11)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=asb_CommunityConsumerandBusinesssegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=asb_CorporateandCommercialSpecialtysegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=asb_RiskManagementandSharedSeriviesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: