Derivative Financial Instruments (Notional and Fair Value of Designated Risk Management Derivative Financial Instruments) (Details) - Asset And Liability Management - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional Value	$ 8,079.5	$ 7,556.0
Fair Value Asset	167.1	198.8
Fair Value Liability	122.0	38.0
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	148.8	104.6
Fair Value Liability	2.7	2.2
Fair Value Hedges \| Securities Available for Sale \| Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	3,274.8	3,042.1
Fair Value Asset	3.5	10.8
Fair Value Liability	39.5	19.8
Cash Flow Hedges \| Forecasted Foreign Currency Denominated Transactions and Investment Securities \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	379.4	367.4
Fair Value Asset	8.5	8.5
Fair Value Liability	9.1	13.8
Cash Flow Hedges \| Securities Available for Sale \| Interest Rate Contracts
Derivative [Line Items]
Notional Value	985.0	935.0
Fair Value Asset	6.3	2.0
Fair Value Liability	0.0	0.7
Net Investment Hedges \| Net Investments in Non-U.S. Affiliates \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	2,190.3	1,961.5
Fair Value Asset	0.0	72.9
Fair Value Liability	$ 70.7	$ 1.5

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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+ 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)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=SL51823488-111719

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=SL51823488-111719

Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

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