Pledged Assets, Accepted Collateral and Restricted Assets (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 10.2
Cash, held in foreign currency	1,800.0		$ 1,800.0
Restricted cash	534.4		531.2
Average deposits maintained to meet Federal Reserve Bank reserve requirements	0.0	$ 0.0
Debt Securities And Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 1,100.0		$ 1,000.0