Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 5,187.4	$ 2,312.4
Gross Amounts Offset in the Balance Sheet	4,890.2	1,618.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	297.2	694.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1.1	0.1
Net Amount	296.1	693.9
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	762.6	1,000.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0
Net Amount	762.6	1,000.6
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	5,950.0	3,313.0
Derivative Liabilities	1,059.8	1,694.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1.1	0.1
Net Amount	1,058.7	1,694.5
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	34.1	489.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	34.1	489.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	34.1	489.7
Other liabilities	3,800.0	3,100.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	5,000.8	2,181.6
Gross Amounts Offset in the Balance Sheet	4,763.3	1,548.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	237.5	633.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1.1	0.1
Net Amount	236.4	632.9
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	160.1	96.7
Gross Amounts Offset in the Balance Sheet	126.9	57.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	33.2	39.4
Net Amount	33.2	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 | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	26.5	33.4
Gross Amounts Offset in the Balance Sheet	0.0	12.5
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	26.5	20.9
Net Amount	$ 26.5	$ 20.9