Derivative Financial Instruments (Notional and Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Derivative [Line Items]
NOTIONAL VALUE	$ 334,688.9	$ 340,241.0
FAIR VALUE, ASSET	3,505.1	1,902.7
Total Gross Derivatives, asset	4,864.1	2,347.4
Less: Netting	1,790.8	1,533.8
Derivative Assets	3,073.3	813.6
FAIR VALUE, LIABILITY	4,316.9	1,566.5
Derivative Liabilities	4,786.2	2,135.2
Less: Netting	3,801.9	1,283.5
Derivative Liabilities	984.3	851.7
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	8,426.0	12,290.2
FAIR VALUE, ASSET	305.4	252.7
FAIR VALUE, LIABILITY	37.1	33.6
Fair Value Hedges \| Derivatives Designated as Hedging under GAAP \| Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	4,584.6	4,430.5
FAIR VALUE, ASSET	32.7	7.6
FAIR VALUE, LIABILITY	21.1	8.7
Fair Value Hedges \| Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	326,262.9	327,950.8
FAIR VALUE, ASSET	4,558.7	2,094.7
FAIR VALUE, LIABILITY	4,749.1	2,101.6
Fair Value Hedges \| Non-Designated Risk Management Derivatives
Derivative [Line Items]
NOTIONAL VALUE	706.9	848.4
FAIR VALUE, ASSET	0.2	0.2
FAIR VALUE, LIABILITY	31.4	38.1
Fair Value Hedges \| Non-Designated Risk Management Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	42.9	109.9
FAIR VALUE, ASSET	0.2	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	664.0	738.5
FAIR VALUE, ASSET	0.0	0.0
FAIR VALUE, LIABILITY	31.1	37.5
Fair Value Hedges \| Client-Related and Trading Derivatives
Derivative [Line Items]
NOTIONAL VALUE	325,556.0	327,102.4
FAIR VALUE, ASSET	4,558.5	2,094.5
FAIR VALUE, LIABILITY	4,717.7	2,063.5
Fair Value Hedges \| Client-Related and Trading Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	314,288.7	315,532.3
FAIR VALUE, ASSET	4,488.3	1,962.1
FAIR VALUE, LIABILITY	4,452.7	1,973.3
Fair Value Hedges \| Client-Related and Trading Derivatives \| Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	11,267.3	11,570.1
FAIR VALUE, ASSET	70.2	132.4
FAIR VALUE, LIABILITY	265.0	90.2
Cash Flow Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	339.6	3,697.9
FAIR VALUE, ASSET	12.8	61.8
FAIR VALUE, LIABILITY	12.0	12.6
Net Investment Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	3,501.8	4,161.8
FAIR VALUE, ASSET	259.9	183.3
FAIR VALUE, LIABILITY	$ 4.0	$ 12.3

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