Derivative Financial Instruments (Notional and Fair Value of Designated Risk Management Derivative Financial Instruments) (Details) - Asset And Liability Management - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Value	$ 7,162.7	$ 6,884.8
Fair Value Asset	182.6	251.7
Fair Value Liability	49.5	48.7
Fair Value Hedges \| Senior Notes and Long-Term Subordinated Debt \| Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	1,250.0	1,250.0
Fair Value Asset	133.0	112.8
Fair Value Liability	2.2	2.0
Fair Value Hedges \| Securities Available for Sale \| Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	2,632.5	2,859.5
Fair Value Asset	3.1	12.7
Fair Value Liability	27.2	28.5
Cash Flow Hedges \| Forecasted Foreign Currency Denominated Transactions \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	387.5	344.9
Fair Value Asset	10.0	6.0
Fair Value Liability	15.9	14.8
Cash Flow Hedges \| Securities Available for Sale \| Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	10.0	10.0
Cash Flow Hedges \| Securities Available for Sale \| Interest Rate Option Contracts
Derivative [Line Items]
Notional Value	925.0	625.0
Fair Value Asset	7.6	1.3
Net Investment Hedges \| Net Investments in Non-U.S. Affiliates \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,957.7	1,795.4
Fair Value Asset	28.9	118.9
Fair Value Liability	$ 4.2	$ 3.4

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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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

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-URI http://asc.fasb.org/extlink&oid=51814546&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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