Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 3,280.7	$ 3,307.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,773.1	3,126.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	507.6	181.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	10.3	12.2
NET AMOUNT	497.3	168.9
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	238.3	260.4
Total Derivatives
GROSS RECOGNIZED ASSETS	3,519.0	3,568.2
Derivative Assets	745.9	441.5
NET AMOUNT	735.6	429.3
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	66,358.2	62,860.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	65,376.6	62,075.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	981.6	784.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	981.6	784.7
NET AMOUNT	0.0	0.0
Other assets excluding derivatives and non financial instruments	10,400.0	10,300.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,814.6	3,006.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,664.5	2,937.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	150.1	69.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	10.3	12.2
NET AMOUNT	139.8	56.9
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	466.1	301.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	108.6	189.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	357.5	111.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	$ 357.5	111.9
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		0.1
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNT		$ 0.1