Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,196.6	$ 1,111.9	$ 3,505.6	$ 3,271.8
Security commissions and trading income	35.5	30.9	107.7	101.7
Other operating income	111.8	68.2	1,097.5	170.2
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	31.0	27.4	95.7	86.3
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 9.7	$ 11.2	$ 29.0	$ 30.5