Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 5,017.8	$ 4,727.8	$ 4,361.8
Security commissions and trading income	170.4	150.5	135.0
Other operating income	207.7	1,157.4	228.7
Securities Commission and Trading
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	162.9	143.7	115.9
Products and Services, Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 41.8	$ 39.3	$ 38.9