Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 2,251.7	$ 3,738.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,090.3	2,817.1
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	161.4	920.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
Net Amount	160.5	920.4
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	449.6	1,144.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0
NET AMOUNT	449.6	1,144.8
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	2,701.3	4,882.8
Derivative Liabilities	611.0	2,065.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
NET AMOUNT	610.1	2,065.2
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	95.6	39.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	95.6	39.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	95.6	39.8
Other liabilities	4,400.0	3,500.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	2,093.4	3,577.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,023.7	2,718.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	69.7	859.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
Net Amount	68.8	858.6
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	123.7	125.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	66.6	98.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	57.1	26.5
Net Amount	57.1	26.5
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES		0.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.0
Net Amount		0.0
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	34.6	35.3
Net Amount	34.6	35.3
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	34.6	35.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	$ 0.0	$ 0.0