Other Operating Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Income and Other Expenses [Line Items]
Business Promotion	$ 27.2	$ 23.4	$ 44.0	$ 50.1
Staff Related	10.3	11.8	26.9	20.5
FDIC Insurance Premiums	3.5	3.2	11.2	8.6
Other Intangibles Amortization	3.4	4.3	11.6	12.6
Other Expenses	36.8	84.3	126.7	182.8
Total Other Operating Expense	81.2	127.0	220.4	274.6
Noninterest Expense	1,128.7	$ 1,094.7	3,367.0	$ 3,197.2
Lower Charges Associated with Account Servicing Activities And A Decline In Other Miscellaneous Expenses
Other Income and Other Expenses [Line Items]
Noninterest Expense	$ 43.4
Lower Account Servicing Activities And Decline In Other Miscellaneous Expenses, Offset By Higher Supplemental Compensation Plan Expense
Other Income and Other Expenses [Line Items]
Noninterest Expense			$ 43.4