Financial Instruments with Off-Balance Sheet Risk (Details) $ in Millions	Sep. 30, 2017 USD ($)
Entity Information [Line Items]
Credit extension commitments	$ 2,100.0
Credit extension commitments beyond one year	721.7
Unused Credit Card Lines
Entity Information [Line Items]
Credit extension commitments	618.1
Standby Letters of Credit
Entity Information [Line Items]
Credit extension commitments	$ 52.6