Goodwill	12 Months Ended
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Goodwill was $1.13 billion for both December 31, 2017 and 2016. Goodwill recorded is primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and acquired and merged organizations. The Corporation recorded goodwill in the amount of $847.7 million related to the merger with Talmer completed on August 31, 2016. During 2015, the Corporation acquired Lake Michigan and Monarch, which resulted in the recognition of goodwill for each transaction of $101.1 million and $5.3 million, respectively. Goodwill is not amortized but is subject to impairment testing annually as of October 31 and on an interim basis if events or changes in circumstances indicate assets might be impaired. Impairment exists when the carrying value of goodwill exceeds its fair value. The Corporation’s most recent annual goodwill impairment review performed as of October 31, 2017 did not indicate that an impairment of goodwill existed. The Corporation also determined that no triggering events have occurred that indicated impairment from the most recent valuation date through December 31, 2017 and that the Corporation's goodwill was not impaired at December 31, 2017.

Goodwill

Goodwill was $1.13 billion for both December 31, 2017 and 2016. Goodwill recorded is primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and acquired and merged organizations. The Corporation recorded goodwill in the amount of $847.7 million related to the merger with Talmer completed on August 31, 2016. During 2015, the Corporation acquired Lake Michigan and Monarch, which resulted in the recognition of goodwill for each transaction of $101.1 million and $5.3 million, respectively.

Goodwill is not amortized but is subject to impairment testing annually as of October 31 and on an interim basis if events or changes in circumstances indicate assets might be impaired. Impairment exists when the carrying value of goodwill exceeds its fair value. The Corporation’s most recent annual goodwill impairment review performed as of October 31, 2017 did not indicate that an impairment of goodwill existed. The Corporation also determined that no triggering events have occurred that indicated impairment from the most recent valuation date through December 31, 2017 and that the Corporation's goodwill was not impaired at December 31, 2017.