Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,557.4	$ 4,162.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,470.4	1,910.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1,087.0	2,252.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	20.6	23.6
NET AMOUNT	1,066.4	2,228.8
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	377.9	1,195.7
Total Derivatives
GROSS RECOGNIZED ASSETS	2,935.3	5,358.5
Derivative Assets	1,464.9	3,448.1
NET AMOUNT	1,444.3	3,424.5
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	65,102.6	65,338.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	64,978.2	64,912.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	124.4	426.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	124.4	426.0
NET AMOUNT	0.0	0.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,197.0	3,801.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,343.7	1,745.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	853.3	2,056.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	20.6	23.6
NET AMOUNT	832.7	2,032.8
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	360.4	359.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	126.7	165.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	233.7	194.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	$ 233.7	194.1
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		1.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		1.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNT		$ 1.9