Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,341.4	$ 1,213.8
Security commissions and trading income	52.1	39.1
Other operating income	70.4	60.3
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	50.4	38.1
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 20.7	$ 20.0