Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,168.4	$ 1,063.7
Security commissions and trading income	36.2	34.8
Other operating income	41.1	54.9
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	31.6	28.7
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 9.7	$ 12.8