Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 4,727.8	$ 4,361.8	$ 4,432.6
Security commissions and trading income	150.5	135.0	136.2
Other operating income	1,157.4	228.7	191.3
Securities Commission and Trading
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	143.7	115.9	116.8
Products and Services, Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 39.3	$ 38.9	$ 37.2