Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Details Textuals)	Jan. 11, 2016 USD ($) complaint	May 22, 2015 USD ($) branch loan_production_office	Dec. 31, 2017 USD ($)	Jul. 28, 2017 complaint	Dec. 31, 2016 USD ($)
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
unfunded commitments			$ 24,000,000		$ 25,000,000
Mortgage loan commitment		$ 196,000,000
Number of branch opening commitments | branch		1
Number of loan production offices | loan_production_office		4
Number of complaints filed under legal proceedings | complaint	2
Conciliation Agreement, Commitment Term		3 years
Loans repurchased under make whole requests			1,000,000		2,000,000
Loans sold to outside investors original amount			10,000,000,000
Loans sold to outside investors remaining outstanding amount			6,100,000,000
Residential mortgage loans sold with recourse risk			44,000,000		62,000,000
Residential mortgage loans sold with credit recourse risk			73,000,000		98,000,000
The Official Committee of Unsecured Creditors of World Marketing Chicago LLC v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 6,000,000
Damages sought, cash	4,000,000
American Funds Service Company v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 600,000
Schumel et al. v. Bank Mutual Corporation et al., Paquin et al. v. Bank Mutual Corporation et al. [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Number of complaints filed under legal proceedings | complaint				2
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Carrying value of investments			147,000,000		68,000,000
Commitments under unconsolidated projects			119,000,000		69,000,000
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Carrying value of investments			$ 23,000,000		$ 17,000,000