Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,078.7	$ 1,111.0	$ 3,390.5	$ 3,250.1
Security commissions and trading income	32.1	36.5	101.1	104.3
Other operating income	57.3	62.3	144.0	171.6
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	27.5	26.1	86.4	82.0
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 8.9	$ 14.0	$ 28.3	$ 39.5