Pledged Assets, Collateral and Restricted Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financial Instruments Owned and Pledged as Collateral [Line Items]
Cash, held in foreign currency	$ 818,900,000		$ 722,200,000
Restricted cash	563,400,000		575,200,000
Average deposits maintained to meet Federal Reserve Bank reserve requirements	0	$ 0
Debt Securities And Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 1,400,000,000		$ 1,100,000,000