Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Repurchase Agreements Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total borrowings, repurchase agreements	$ 531.9	$ 39.8
Allowance for credit losses, available-for-sale securities	531.9	39.8
Amounts related to agreements not included in Note 28	0.0	0.0
U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total borrowings, repurchase agreements	531.9	39.8
OVERNIGHT AND CONTINUOUS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total borrowings, repurchase agreements	32.4	39.8
Allowance for credit losses, available-for-sale securities	32.4	39.8
Amounts related to agreements not included in Note 28	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]
Total borrowings, repurchase agreements	32.4	39.8
UP TO 30 DAYS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total borrowings, repurchase agreements	499.5	0.0
Allowance for credit losses, available-for-sale securities	499.5	0.0
Amounts related to agreements not included in Note 28	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]
Total borrowings, repurchase agreements	$ 499.5	$ 0.0