Other Borrowings - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Debt [Line Items]
FHLB advances	$ 0.0	$ 5.0
Other Short-term Borrowings	35.3	0.0
Subordinated Long-term Debt, Noncurrent	815.1	469.8
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	80.7	78.9
FHLB advances	$ 0.0	5.0
Senior Notes
Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.50%
Debt Instrument, Face Amount	$ 300.0
Credit Linked Notes Maturing December 2024 [Member]
Debt [Line Items]
Debt Instrument, Face Amount	242.0
Debt Issuance Cost	$ 2.9
Debt Instrument, Interest Rate Terms	LIBOR plus 5.50%
Federal Home Loan Bank Advances [Member]
Debt [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	$ 7,800.0	4,000.0
FRB [Member]
Debt [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	3,400.0	$ 2,700.0
Unsecured Credit Facility [Member]
Debt [Line Items]
Secured borrowing credit line	2,800.0
Warehouse Agreement Borrowings
Debt [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	$ 1,000.0

Face (par) amount of debt instrument at time of issuance.

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