Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,231.6	$ 3,151.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,807.6	2,810.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	424.0	340.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	5.3	5.0
NET AMOUNT	418.7	335.5
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	360.0	581.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	360.0	581.2
Total Derivatives
GROSS RECOGNIZED ASSETS	2,591.6	3,732.4
Derivative Assets	784.0	921.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	5.3	5.0
NET AMOUNT	778.7	916.7
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	23,032.4	12,494.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	21,975.0	11,423.9
Securities Purchased under Agreements to Resell	1,057.4	1,070.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1,057.4	1,070.3
Other assets excluding derivatives and non financial instruments	9,600.0	8,900.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	1,955.0	2,928.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,601.1	2,666.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	353.9	262.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	5.3	5.0
NET AMOUNT	348.6	257.5
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	276.2	217.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	206.5	144.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	69.7	73.3
NET AMOUNT	69.7	73.3
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	0.0	4.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.0	4.4
NET AMOUNT	0.0	4.4
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	0.4	0.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.4	0.3
NET AMOUNT	$ 0.4	$ 0.3