Recent Development Recent Development Details (Notes)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	Note 23 Recent Developments On February 1, 2018, the Corporation acquired Bank Mutual Corporation ("Bank Mutual") pursuant to an Agreement and Plan of Merger, dated as of July 20, 2017 (the "Merger Agreement"), under which Bank Mutual merged with and into the Corporation. Under the terms of the Merger Agreement, Bank Mutual’s shareholders received 0.422 shares of Corporation common stock for each share of Bank Mutual’s common stock. The Corporation expects to issue approximately 19.6 million shares for a total deal value of approximately $485 million based on the closing sale price of a share of Associated common stock on January 31, 2018. We expect to merge Bank Mutual's banking subsidiary into Associated Bank in late June or July 2018.