Offsetting of Assets and Liabilities - Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 3,307.8	$ 3,151.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	3,126.7	2,810.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	181.1	340.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	12.2	5.0
NET AMOUNT	168.9	335.5
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	260.4	581.2
Total Derivatives
GROSS RECOGNIZED ASSETS	3,568.2	3,732.4
Derivative Asset	441.5	921.7
NET AMOUNT	429.3	916.7
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	62,860.2	12,494.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	62,075.5	11,423.9
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	784.7	1,070.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	1,070.3
NET AMOUNT	784.7	0.0
Other assets (excluding derivative assets)	10,300.0	8,900.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	3,006.3	2,928.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,937.2	2,666.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	69.1	262.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	12.2	5.0
NET AMOUNT	56.9	257.5
Interest Rate Swaps | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	301.4	217.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	189.5	144.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	111.9	73.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	111.9	73.3
Interest Rate Swaps | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	0.1	4.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.1	4.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	$ 0.1	4.4
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		0.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNT		$ 0.3