Pledged and Restricted Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Cash, held in foreign currency	$ 529,100,000		$ 330,400,000
Restricted cash	569,600,000		574,200,000
Average deposits maintained to meet Federal Reserve Bank reserve requirements	0	$ 0
Collateral that may be repledged or sold
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	44,600,000,000		43,200,000,000
Asset Pledged as Collateral with Right
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	365,000,000		464,700,000
Collateral Requirements | Collateral that may be repledged or sold
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	$ 13,300,000,000		$ 8,700,000,000