Pledged Assets, Accepted Collateral and Restricted Assets (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Financial Instruments Owned and Pledged as Collateral [Line Items]
Cash, held in foreign currency	$ 1,100,000,000	$ 722,200,000
Restricted cash	491,200,000	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	$ 1,200,000,000	$ 1,100,000,000