Derivative Financial Instruments (Notional and Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Derivative [Line Items]
NOTIONAL VALUE	$ 312,069.9	$ 340,241.0
FAIR VALUE, ASSET	4,975.0	1,902.7
Total Gross Derivatives, asset	6,360.1	2,347.4
Less: Netting	2,482.8	1,533.8
Derivative Assets	3,877.3	813.6
FAIR VALUE, LIABILITY	5,994.4	1,566.5
Derivative Liabilities	6,158.5	2,135.2
Less: Netting	5,268.1	1,283.5
Derivative Liabilities	890.4	851.7
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	8,245.1	12,290.2
FAIR VALUE, ASSET	598.5	252.7
FAIR VALUE, LIABILITY	73.0	33.6
Fair Value Hedges \| Derivatives Designated as Hedging under GAAP \| Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	4,628.2	4,430.5
FAIR VALUE, ASSET	67.1	7.6
FAIR VALUE, LIABILITY	49.5	8.7
Fair Value Hedges \| Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	303,824.8	327,950.8
FAIR VALUE, ASSET	5,761.6	2,094.7
FAIR VALUE, LIABILITY	6,085.5	2,101.6
Fair Value Hedges \| Non-Designated Risk Management Derivatives
Derivative [Line Items]
NOTIONAL VALUE	670.5	848.4
FAIR VALUE, ASSET	2.8	0.2
FAIR VALUE, LIABILITY	27.9	38.1
Fair Value Hedges \| Non-Designated Risk Management Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	51.4	109.9
FAIR VALUE, ASSET	0.9	0.2
FAIR VALUE, LIABILITY	0.3	0.6
Fair Value Hedges \| Non-Designated Risk Management Derivatives \| Other Financial Derivatives
Derivative [Line Items]
NOTIONAL VALUE	619.1	738.5
FAIR VALUE, ASSET	1.9	0.0
FAIR VALUE, LIABILITY	27.6	37.5
Fair Value Hedges \| Client-Related and Trading Derivatives
Derivative [Line Items]
NOTIONAL VALUE	303,154.3	327,102.4
FAIR VALUE, ASSET	5,758.8	2,094.5
FAIR VALUE, LIABILITY	6,057.6	2,063.5
Fair Value Hedges \| Client-Related and Trading Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	291,383.1	315,532.3
FAIR VALUE, ASSET	5,618.4	1,962.1
FAIR VALUE, LIABILITY	5,637.8	1,973.3
Fair Value Hedges \| Client-Related and Trading Derivatives \| Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	11,771.2	11,570.1
FAIR VALUE, ASSET	140.4	132.4
FAIR VALUE, LIABILITY	419.8	90.2
Cash Flow Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	224.5	3,697.9
FAIR VALUE, ASSET	17.4	61.8
FAIR VALUE, LIABILITY	13.7	12.6
Net Investment Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	3,392.4	4,161.8
FAIR VALUE, ASSET	514.0	183.3
FAIR VALUE, LIABILITY	$ 9.8	$ 12.3

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