Derivative Financial Instruments (Notional and Fair Values of Client-Related and Trading Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value	$ 315,049.9	$ 337,617.7
Fair value asset	2,512.9	2,203.3
Total Gross Derivatives, asset	3,409.4	2,654.1
Less: Netting	1,775.8	1,860.0
Derivative Asset	1,633.6	794.1
Fair value liability	2,717.2	2,003.1
Total Gross Derivatives, liabilities	3,213.2	2,829.0
Less: Netting	2,463.3	1,621.4
Derivative Liabilities	749.9	1,207.6
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
Notional Value	11,493.4	11,698.4
Fair value asset	285.0	60.9
Fair value liability	31.3	211.9
Fair Value Hedges \| Derivatives Designated as Hedging under GAAP \| Interest Rate Contracts
Derivative [Line Items]
Notional Value	4,457.4	4,473.1
Fair value asset	33.3	31.7
Fair value liability	20.7	18.2
Fair Value Hedges \| Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
Notional Value	303,556.5	325,919.3
Fair value asset	3,124.4	2,593.2
Fair value liability	3,181.9	2,617.1
Fair Value Hedges \| Non-Designated Risk Management Derivatives
Derivative [Line Items]
Notional Value	608.3	618.8
Fair value asset	0.4	1.1
Fair value liability	37.6	30.5
Fair Value Hedges \| Non-Designated Risk Management Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	139.5	214.1
Fair value asset	0.4	1.1
Fair value liability	0.9	0.1
Fair Value Hedges \| Non-Designated Risk Management Derivatives \| Other Financial Derivatives
Derivative [Line Items]
Notional Value	468.8	404.7
Fair value asset	0.0	0.0
Fair value liability	36.7	30.4
Fair Value Hedges \| Client-Related and Trading Derivatives
Derivative [Line Items]
Notional Value	302,948.2	325,300.5
Fair value asset	3,124.0	2,592.1
Fair value liability	3,144.3	2,586.6
Fair Value Hedges \| Client-Related and Trading Derivatives \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	295,355.2	317,882.5
Fair value asset	3,056.9	2,527.0
Fair value liability	3,053.8	2,522.5
Fair Value Hedges \| Client-Related and Trading Derivatives \| Interest Rate Contracts
Derivative [Line Items]
Notional Value	7,593.0	7,418.0
Fair value asset	67.1	65.1
Fair value liability	90.5	64.1
Cash Flow Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	3,196.8	3,289.0
Fair value asset	60.2	28.4
Fair value liability	7.5	13.0
Cash Flow Hedges \| Derivatives Designated as Hedging under GAAP \| Interest Rate Contracts
Derivative [Line Items]
Notional Value	925.0	925.0
Fair value asset	0.2	0.2
Fair value liability	2.2	1.2
Net Investment Hedges \| Derivatives Designated as Hedging under GAAP \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	2,914.2	3,011.3
Fair value asset	191.3	0.6
Fair value liability	$ 0.9	$ 179.5

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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