Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 1,265.5	$ 1,196.6	$ 3,710.4	$ 3,505.6
Foreign Exchange Trading Income	57.2	54.1	166.5	169.5
Treasury Management Fees	9.5	8.2	28.8	26.5
Security Commissions and Trading Income	41.8	35.5	120.5	107.7
Other Operating Income	60.6	111.8	167.7	1,097.5
Investment Security Gains (Losses), net	0.0	0.0	0.0	(189.3)
Total Other Noninterest Income	169.1	209.6	483.5	1,211.9
Total Noninterest Income	1,434.6	1,406.2	4,193.9	4,717.5
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	515.5	482.5	1,499.0	1,427.1
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	668.3	634.8	1,965.3	1,838.3
Securities Lending
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	21.5	17.7	59.7	53.2
Other
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 60.2	$ 61.6	$ 186.4	$ 187.0