Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,063.6	$ 1,168.4
Security commissions and trading income	34.7	36.2
Other operating income	46.8	41.1
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	29.9	31.6
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 9.1	$ 9.7