Revenue from Contracts with Clients (Narrative) (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
Security commissions and trading income	55.6	39.6	107.7	78.7
Other operating income	594.2	66.1	664.7	126.4
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	53.1	37.7	103.6	75.8
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 19.3	$ 20.1	$ 40.1	$ 40.1