Other Assets - Affordable Housing and Other Tax Credit Investment Partnerships (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Affordable housing and other tax credit investment partnership interests
Investment partnership interest	$ 269.0		$ 235.5
Investment, Proportional Amortization Method, Elected, Statement of Financial Position [Extensible Enumeration]	Other Assets		Other Assets
Amortization	$ 7.6	$ 7.7
Investment Program, Proportional Amortization Method, Applied, Amortization Expense, Statement of Income or Comprehensive Income [Extensible Enumeration]	Income Tax Expense (Benefit)	Income Tax Expense (Benefit)
Affordable housing tax credits and other benefits recognized	$ 9.6	$ 9.6
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)
Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization, Statement of Cash Flows [Extensible Enumeration]	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
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	$ 133.3		$ 98.7