Financial Instruments with Off-Balance Sheet Risk (Details) $ in Millions	Jun. 30, 2018 USD ($)
Entity Information [Line Items]
Credit extension commitments	$ 2,190.2
Credit extension commitments beyond one year	816.2
Unused Credit Card Lines
Entity Information [Line Items]
Credit extension commitments	681.1
Standby Letters of Credit
Entity Information [Line Items]
Credit extension commitments	$ 47.6