Related Party Transactions (Related Party Transactions - Additional Information) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Related Party Transactions
Gain on sale of Worldpay, Inc. shares		$ (205.0)	$ 0.0
Vantiv Holding, LLC
Related Party Transactions
Class B common shares held in Worldpay, Inc,	$ 10.3	$ 10.3
Equity Method Investment, Ownership Percentage	3.30%	3.30%		4.90%	8.60%
Gain in noninterest income as a result of Worldpay Transaction		$ 414.0
Equity method investments, carrying value	$ 426.0	426.0
Gain on sale of Worldpay, Inc. shares	$ (205.0)
Class A common shares sold	5,000,000
GS Holdings
Related Party Transactions
Gain in noninterest income subsequemt to GreenSky, Inc IPO	$ 16.0
Investment in Equity Securities	$ 53.0	$ 53.0
Class A common stock shares issued at IPO	38,000,000	38,000,000
Class A common stock valuation	$ 23	$ 23
Economic interest percentage	1.40%	1.40%
Membership units that were converted to GS Holdings units	252,550	252,550
Class B common shares held in GreenSky, Inc.	2,525,498	2,525,498