Other Assets - Affordable Housing and Other Tax Credit Investment Partnerships (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Affordable housing and other tax credit investment partnership interests
Investment partnership interest	$ 222.3		$ 222.3		$ 206.9
Investment, Proportional Amortization Method, Elected, Statement of Financial Position [Extensible Enumeration]	Other Assets		Other Assets		Other Assets
Amortization	$ 7.5	$ 6.1	$ 15.2	$ 12.2
Investment Program, Proportional Amortization Method, Applied, Amortization Expense, Statement of Cash Flows [Extensible Enumeration]	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Investment Program, Proportional Amortization Method, Applied, Amortization Expense, Statement of Income or Comprehensive Income [Extensible Enumeration]	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)
Affordable housing tax credits and other benefits recognized	$ 9.6	$ 7.7	$ 19.2	$ 15.1
Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization, Statement of Income or Comprehensive Income [Extensible Enumeration]	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Affordable housing and other tax credit investment partnership interests
Unfunded commitments to fund low-income housing partnerships	$ 92.2		$ 92.2		$ 80.7