Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,143.4	$ 1,075.4	$ 2,311.8	$ 2,139.1
Security commissions and trading income	32.8	33.0	69.0	67.8
Other operating income	45.6	54.4	86.7	109.3
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	27.3	27.2	58.9	55.9
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 9.7	$ 12.7	$ 19.4	$ 25.5