Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,470.7	$ 3,151.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,553.1	2,810.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	917.6	340.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5.0
NET AMOUNT	903.3	335.5
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	942.3	581.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	942.3	581.2
Total Derivatives
GROSS RECOGNIZED ASSETS	3,413.0	3,732.4
Derivative Assets	1,859.9	921.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5.0
NET AMOUNT	1,845.6	916.7
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	50,143.2	12,494.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	49,758.9	11,423.9
Securities Purchased under Agreements to Resell	384.3	1,070.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	384.3	1,070.3
Other assets excluding derivatives and non financial instruments	10,700.0	8,900.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,106.8	2,928.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,266.6	2,666.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	840.2	262.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5.0
NET AMOUNT	825.9	257.5
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	363.9	217.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	286.5	144.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	77.4	73.3
NET AMOUNT	$ 77.4	73.3
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		4.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		4.4
NET AMOUNT		4.4
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
NET AMOUNT		$ 0.3