Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters (Details Textuals)	Jan. 11, 2016 USD ($) complaint	May 22, 2015 USD ($) branch loan_production_office	Sep. 30, 2017 USD ($)	Sep. 06, 2017 complaint	Aug. 30, 2017 complaint	Jul. 28, 2017 complaint	Dec. 31, 2016 USD ($)
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Unfunded commitments			$ 24,000,000				$ 25,000,000
Carrying value of investments			142,000,000				85,000,000
Commitments under unconsolidated projects			101,000,000				69,000,000
Number of complaints filed under legal proceedings | complaint	2
Commitment term		3 years
Mortgage loan commitment		$ 196,000,000
Number of branch opening commitments | branch		1
Number of loan production offices | loan_production_office		4
Conciliation agreement cost, commitment term		4 years
Loans repurchased under make whole requests			1,000,000				2,000,000
Loans sold to outside investors original amount			9,700,000,000
Loans sold to outside investors remaining outstanding amount			6,100,000,000
Residential mortgage loans sold with recourse risk			77,000,000				62,000,000
Residential mortgage loans sold with credit recourse risk			$ 79,000,000				$ 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, and Paquin et al v. Bank Mutual Corporation et al [Domain]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Number of complaints filed under legal proceedings | complaint						2
Wollenburg 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					1
Parshall 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				1