Variable Interest Entities (Income Tax Credits and Other Tax Benefits and Amortization Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	$ 114.0	$ 107.1	$ 113.9
Income tax credits and other income tax benefits associated with tax credit investments, statements of cash flows location not disclosed	Total Income Tax Credits and Other Income Tax Benefits	Total Income Tax Credits and Other Income Tax Benefits	Total Income Tax Credits and Other Income Tax Benefits
Income tax credits and other income tax benefits associated with tax credit investments, statements of income location	Provision for Income Taxes	Provision for Income Taxes	Provision for Income Taxes
Amortization Expense	$ 98.5	$ 89.3	$ 96.5
Amortization associated with unconsolidated tax credit investments, statements of income location	Noninterest Expense	Noninterest Expense	Noninterest Expense
Amortization expense, statements of cash flows location not disclosed	Total Amortization Expense	Total Amortization Expense	Total Amortization Expense
Affordable Housing
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	$ 97.3	$ 87.0	$ 89.3
Amortization Expense	83.4	71.8	76.8
New Markets
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	16.7	20.1	24.6
Amortization Expense	$ 15.1	$ 17.5	$ 19.7