Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 1,327.3	$ 3,307.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	914.2	3,126.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	413.1	181.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	3.6	12.2
NET AMOUNT	409.5	168.9
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	433.8	260.4
Total Derivatives
GROSS RECOGNIZED ASSETS	1,761.1	3,568.2
Derivative Assets	846.9	441.5
NET AMOUNT	843.3	429.3
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	66,364.6	62,860.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	65,864.5	62,075.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	500.1	784.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	500.1	784.7
NET AMOUNT	0.0	0.0
Other assets excluding derivatives and non financial instruments	10,200.0	10,300.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	923.3	3,006.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	699.0	2,937.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	224.3	69.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	3.6	12.2
NET AMOUNT	220.7	56.9
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	399.5	301.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	215.2	189.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	184.3	111.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	184.3	111.9
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	4.5	0.1
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	4.5	0.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	$ 4.5	$ 0.1