Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,213.8	$ 1,142.9
Security commissions and trading income	39.1	37.9
Other operating income	50.7	61.0
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	38.1	33.7
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 10.4	$ 9.3