Securities Sold Under Agreements to Repurchase (Repurchase Agreements Accounted for as Secured Borrowings) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 329.7	$ 531.9
Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23	329.7	531.9
Amounts related to agreements not included in Note 23	0.0	0.0
U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	329.7	531.9
OVERNIGHT AND CONTINUOUS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	329.7	32.4
Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23	329.7	32.4
Amounts related to agreements not included in Note 23	0.0	0.0
OVERNIGHT AND CONTINUOUS | U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	329.7	32.4
UP TO 30 DAYS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	0.0	499.5
Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23	0.0	499.5
Amounts related to agreements not included in Note 23	0.0	0.0
UP TO 30 DAYS | U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 0.0	$ 499.5