Derivative Financial Instruments (Fair And Notional Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ 15,264.6	$ 13,128.8
Asset Fair Value	68.7	111.6
Liability Fair Value	(87.0)	(68.8)
Total Return Swap (TRS)
Derivatives, Fair Value [Line Items]
Notional Amount	182.4	587.5
Qualifying Hedges
Derivatives, Fair Value [Line Items]
Notional Amount	977.3	817.9
Asset Fair Value	0.2	16.9
Liability Fair Value	(18.7)	0.0
Qualifying Hedges \| Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Notional Amount	977.3	817.9
Asset Fair Value	0.2	16.9
Liability Fair Value	(18.7)	0.0
Non-Qualifying Hedges
Derivatives, Fair Value [Line Items]
Notional Amount	14,287.3	12,310.9
Asset Fair Value	68.5	94.7
Liability Fair Value	(68.3)	(68.8)
Non-Qualifying Hedges \| Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Notional Amount	1,375.5	1,329.8
Asset Fair Value	6.9	30.2
Liability Fair Value	(14.9)	(6.0)
Non-Qualifying Hedges \| Interest rate swaps
Derivatives, Fair Value [Line Items]
Notional Amount	7,112.0	5,309.2
Asset Fair Value	60.8	63.0
Liability Fair Value	(38.6)	(50.1)
Non-Qualifying Hedges \| Options \| Written
Derivatives, Fair Value [Line Items]
Notional Amount	2,744.3	2,626.5
Asset Fair Value	0.0	0.1
Liability Fair Value	(0.7)	(1.0)
Non-Qualifying Hedges \| Options \| Purchased
Derivatives, Fair Value [Line Items]
Notional Amount	2,571.5	2,129.6
Asset Fair Value	0.7	1.0
Liability Fair Value	0.0	(0.1)
Non-Qualifying Hedges \| Total Return Swap (TRS)
Derivatives, Fair Value [Line Items]
Notional Amount	182.4	587.5
Asset Fair Value	0.0	0.0
Liability Fair Value	(14.1)	(11.3)
Non-Qualifying Hedges \| Equity Warrants
Derivatives, Fair Value [Line Items]
Notional Amount	0.8	1.0
Asset Fair Value	0.0	0.2
Liability Fair Value	0.0	0.0
Non-Qualifying Hedges \| Interest Rate Lock Commitments
Derivatives, Fair Value [Line Items]
Notional Amount	7.7	20.7
Asset Fair Value	0.1	0.1
Liability Fair Value	0.0	(0.1)
Non-Qualifying Hedges \| Forward sale commitments on agency MBS
Derivatives, Fair Value [Line Items]
Notional Amount	8.0	39.0
Asset Fair Value	0.0	0.1
Liability Fair Value	0.0	0.0
Non-Qualifying Hedges \| Credit derivatives
Derivatives, Fair Value [Line Items]
Notional Amount	285.1	267.6
Asset Fair Value	0.0	0.0
Liability Fair Value	$ 0.0	$ (0.2)

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=84234895&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=82849420&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=82924980&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=82924980&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
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-Topic 815
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

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