Financial Instruments with Off-Balance Sheet Risk (Details) $ in Millions	Sep. 30, 2018 USD ($)
Entity Information [Line Items]
Credit extension commitments	$ 2,515.4
Credit extension commitments beyond one year	942.1
Unused Credit Card Lines
Entity Information [Line Items]
Credit extension commitments	701.8
Standby Letters of Credit
Entity Information [Line Items]
Credit extension commitments	$ 45.0