Pending Acquisition (Additional Information) (Detail) - USD ($) $ / shares in Units, $ in Billions	6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Business Acquisition
MB Financial Total Assets at 3/31/2018		$ 20.0
May 18, 2018
Business Acquisition
Total implied consideration transferred	$ 54.2
Share consideration transferred	1.45
Implied value of merger transaction	$ 4.7
Cash consideration transferred per share	$ 5.54