Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,111.9	$ 1,078.7	$ 3,271.8	$ 3,390.5
Security commissions and trading income	30.9	32.1	101.7	101.1
Other operating income	68.2	57.3	170.2	144.0
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	27.4	27.5	86.3	86.4
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 11.2	$ 8.9	$ 30.5	$ 28.3