Offsetting of Assets and Liabilities - Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 1,791.3	$ 4,162.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,779.2	1,910.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	12.1	2,252.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	2.7	23.6
Derivative Assets	9.4	2,228.8
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	303.0	1,195.7
Total Derivatives
GROSS RECOGNIZED ASSETS	2,094.3	5,358.5
Derivative Asset	315.1	3,448.1
NET AMOUNT	312.4	3,424.5
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	92,669.7	65,338.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	90,015.6	64,912.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	2,654.1	426.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	2,654.1	426.0
NET AMOUNT	0.0	0.0
Derivative
Securities Purchased under Agreements to Resell
Collateral that may be repledged or sold	2.7	23.6
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	1,707.2	3,801.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,696.1	1,745.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	11.1	2,056.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	2.7	23.6
Derivative Assets	8.4	2,032.8
Interest Rate Swaps | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	83.4	359.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	82.4	165.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1.0	194.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
Derivative Assets	1.0	194.1
Interest Rate Swaps | 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
Derivative Assets		$ 1.9
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	0.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0
Derivative Assets	$ 0.0