Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,545.8	$ 1,902.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,176.6	1,533.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	369.2	368.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.7	2.8
NET AMOUNT	368.5	366.1
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	721.1	444.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	721.1	444.7
Total Derivatives
GROSS RECOGNIZED ASSETS	3,266.9	2,347.4
Derivative Assets	1,090.3	813.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.7	2.8
NET AMOUNT	1,089.6	810.8
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	2,678.0	2,078.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,646.6	1,392.5
Securities Purchased under Agreements to Resell	1,031.4	686.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1,031.4	686.4
Other assets excluding derivatives and non financial instruments	7,600.0	7,800.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,464.1	1,762.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,153.9	1,530.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	310.2	232.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.7	2.8
NET AMOUNT	309.5	229.2
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	81.5	140.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	22.7	3.1
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	58.8	136.9
NET AMOUNT	58.8	$ 136.9
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	0.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.2
NET AMOUNT	$ 0.2