Recent Development (Details)	Jul. 20, 2017 shares
Bank Mutual [Member]
Recent Developments [Line Items]
Consideration shares transferred	0.422

Shares transferred at acquisition-date in consideration of business combination.

No definition available.

Name:	asb_BusinessCombinationConsiderationSharesTransferred
Namespace Prefix:	asb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration