Derivative Financial Instruments (Notional and Fair Value of Designated Risk Management Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Fair value asset	$ 1,530.3	$ 3,047.6
Fair value liability	1,386.3	2,767.6
Asset And Liability Management
Derivative [Line Items]
Notional Value	9,680.7	9,942.9
Fair value asset	67.8	494.8
Fair value liability	58.9	42.2
Asset And Liability Management \| 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	29.7	71.8
Fair value liability	3.5	3.3
Asset And Liability Management \| Fair Value Hedges \| Available for Sale Investment Securities \| Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	3,670.3	3,873.4
Fair value asset	9.6	88.3
Fair value liability	11.0	16.8
Asset And Liability Management \| Cash Flow Hedges \| Forecasted Foreign Currency Denominated Transactions \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	351.5	329.3
Fair value asset	10.2	8.5
Fair value liability	6.2	7.8
Asset And Liability Management \| Cash Flow Hedges \| Foreign Currency Denominated Investment Securities \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,193.9	1,431.6
Fair value asset	0.0	151.5
Fair value liability	27.7	0.8
Asset And Liability Management \| Cash Flow Hedges \| Available for Sale Investment Securities \| Interest Rate Contracts
Derivative [Line Items]
Notional Value	1,025.0	975.0
Fair value asset	0.2	0.1
Fair value liability	3.0	2.7
Asset And Liability Management \| Net Investment Hedges \| Net Investments in Non-U.S. Affiliates \| Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	2,190.0	2,083.6
Fair value asset	18.1	174.6
Fair value liability	$ 7.5	$ 10.8

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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