Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 2,143.8	$ 2,312.4
Gross Amounts Offset in the Balance Sheet	1,603.3	1,618.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	540.5	694.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.1
Net Amount	540.5	693.9
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	357.0	1,000.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0
Net Amount	357.0	1,000.6
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	2,500.8	3,313.0
Derivative Liabilities	897.5	1,694.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.1
Net Amount	897.5	1,694.5
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	269.8	489.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	269.8	489.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	269.8	489.7
Other liabilities	3,600.0	3,100.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	1,969.2	2,181.6
Gross Amounts Offset in the Balance Sheet	1,493.6	1,548.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	475.6	633.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.1
Net Amount	475.6	632.9
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	142.3	96.7
Gross Amounts Offset in the Balance Sheet	109.7	57.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	32.6	39.4
Net Amount	32.6	39.4
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES		0.7
Gross Amounts Offset in the Balance Sheet		0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.7
Net Amount		0.7
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	32.3	20.9
Net Amount	32.3	20.9
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	32.3	33.4
Gross Amounts Offset in the Balance Sheet	$ 0.0	$ 12.5