Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,096.3	$ 1,143.4	$ 2,159.9	$ 2,311.8
Security commissions and trading income	36.1	32.8	70.8	69.0
Other operating income	55.2	45.6	102.0	86.7
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	29.0	27.3	58.9	58.9
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 10.2	$ 9.7	$ 19.3	$ 19.4