Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,004.0	$ 4,097.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	886.8	3,507.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1,117.2	589.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.9	0.9
NET AMOUNT	1,102.3	588.5
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	812.3	461.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	812.3	461.0
Total Derivatives
GROSS RECOGNIZED ASSETS	2,816.3	4,558.2
Derivative Assets	1,929.5	1,050.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.9	0.9
NET AMOUNT	1,914.6	1,049.5
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	947.8	1,596.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	947.8	1,596.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	947.8	1,596.5
Other assets excluding derivatives and non financial instruments	7,500.0	7,300.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	1,796.6	3,799.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	884.1	3,505.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	912.5	294.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.9	0.9
NET AMOUNT	897.6	293.5
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	204.9	295.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2.7	2.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	202.2	293.4
NET AMOUNT	202.2	293.4
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2.5	1.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	2.5	1.6
NET AMOUNT	$ 2.5	$ 1.6