Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,265.5	$ 1,196.6	$ 3,710.4	$ 3,505.6
Security commissions and trading income	41.8	35.5	120.5	107.7
Other operating income	60.6	111.8	167.7	1,097.5
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	39.5	31.0	115.3	95.7
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 10.4	$ 9.7	$ 31.2	$ 29.0