Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 2,509.1	$ 3,738.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,333.9	2,817.1
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	175.2	920.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.5	0.5
Net Amount	174.7	920.4
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	247.6	1,144.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0
NET AMOUNT	247.6	1,144.8
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	2,756.7	4,882.8
Derivative Liabilities	422.8	2,065.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.5	0.5
NET AMOUNT	422.3	2,065.2
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	1,073.6	39.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	500.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	573.6	39.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	573.6	39.8
Other liabilities	4,700.0	3,500.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	2,365.1	3,577.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,268.8	2,718.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	96.3	859.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.5	0.5
Net Amount	95.8	858.6
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	106.3	125.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	65.1	98.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	41.2	26.5
Net Amount	41.2	26.5
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	1.0	0.0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1.0	0.0
Net Amount	1.0	0.0
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	36.7	35.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	36.7	35.3
Net Amount	$ 36.7	$ 35.3