Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 1,349.5	$ 1,231.1	$ 2,690.9	$ 2,444.9
Foreign Exchange Trading Income	97.1	50.6	184.8	109.3
Security Commissions and Trading Income	55.6	39.6	107.7	78.7
Other Operating Income	594.2	66.1	664.7	126.4
Investment Security Gains (Losses), net	(73.9)	0.0	(73.9)	0.0
Total Other Noninterest Income	673.0	156.3	883.3	314.4
Total Noninterest Income	2,022.5	1,387.4	3,574.2	2,759.3
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	544.9	498.4	1,076.5	983.5
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	712.3	649.6	1,429.7	1,297.0
Securities Lending
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	29.6	20.3	53.2	38.2
Other
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 62.7	$ 62.8	$ 131.5	$ 126.2