Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Financial Assets
Gross Amounts Recognized	$ 40.2		$ 40.2		$ 45.2
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	40.2		40.2		45.2
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	36.4		36.4		45.1
Net Amount	3.8		3.8		0.1
Financial Liabilities
Gross Amounts Recognized	163.1		163.1		159.6
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	163.1		163.1		159.6
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	163.1		163.1		159.6
Repurchase agreements
Gross Amounts Recognized	929.9		929.9		1,052.9
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	929.9		929.9		1,052.9
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	929.9		929.9		1,052.9
Net Amount	0.0		0.0		0.0
Total assets and liabilities
Gross Amounts Recognized	1,093.0		1,093.0		1,212.5
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	1,093.0		1,093.0		1,212.5
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	929.9		929.9		1,052.9
Net Amount	163.1		163.1		159.6
Derivative Liability, Notional Amount	2,914.5		2,914.5		2,449.0
Not Designated as Hedging Instrument
Total assets and liabilities
Amount of net gains recognized in mortgage banking revenues	0.2	$ 1.0	0.2	$ 1.5
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	40.2		40.2		45.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	40.2		40.2		45.1
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	36.4		36.4		45.1
Net Amount	3.8		3.8		0.0
Financial Liabilities
Gross Amounts Recognized	163.0		163.0		159.6
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	163.0		163.0		159.6
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	163.0		163.0		159.6
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,645.7		1,645.7		1,728.1
Mortgage Related Derivatives
Financial Assets
Gross Amounts Recognized					0.1
Gross Amounts Offset in the Balance Sheet					0.0
Net Amounts in the Balance Sheet					0.1
Financial Instruments					0.0
Fair Value of Financial Collateral in the Balance Sheet					0.0
Net Amount					0.1
Risk Participation Agreements | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	103.7		103.7		106.1
Interest Rate Lock Commitments
Financial Liabilities
Gross Amounts Recognized	0.1		0.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	0.1		0.1
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0
Net Amount	0.1		0.1
Interest Rate Lock Commitments | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	$ 15.1		$ 15.1		$ 14.8