Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 05, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-31343
Entity Registrant Name	ASSOCIATED BANC-CORP
Entity Incorporation, State or Country Code	WI
Entity Tax Identification Number	39-1098068
Entity Address, Address Line One	433 Main Street
Entity Address, City or Town	Green Bay,
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	54301
City Area Code	920
Local Phone Number	491-7500
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 2,058,439,343
Entity Common Stock, Shares Outstanding		152,831,898
Documents Incorporated by Reference	Portions of the registrant's Proxy Statement for the Annual Meeting of Shareholders to held on April 27, 2021 are incorporated by reference in this Form 10-K into Part III.
Entity Central Index Key	0000007789
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Amendment Flag	false
NEW YORK STOCK EXCHANGE, INC.
Entity Information [Line Items]
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	ASB
Security Exchange Name	NYSE
Series C Preferred Stock | NEW YORK STOCK EXCHANGE, INC.
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shrs, each representing 1/40th intrst in a shr of 6.125% Non-Cum. Perp Pref Stock, Srs C
Trading Symbol	ASB PrC
Security Exchange Name	NYSE
Series D Preferred Stock | NEW YORK STOCK EXCHANGE, INC.
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shrs, each representing 1/40th intrst in a shr of 5.375% Non-Cum. Perp Pref Stock, Srs D
Trading Symbol	ASB PrD
Security Exchange Name	NYSE
Series E Preferred Stock | NEW YORK STOCK EXCHANGE, INC.
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shrs, each representing 1/40th intrst in a shr of 5.875% Non-Cum. Perp Pref Stock, Srs E
Trading Symbol	ASB PrE
Security Exchange Name	NYSE
Series F Preferred Stock [Member] | NEW YORK STOCK EXCHANGE, INC.
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shrs, each representing 1/40th intrst in a shr of 5.625% Non-Cum. Perp Pref Stock, Srs F
Trading Symbol	ASB PrF
Security Exchange Name	NYSE