Derivative Financial Instruments (Fair and Notional Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ 14,412.7	$ 13,128.8
Asset Fair Value	79.4	111.6
Liability Fair Value	(115.0)	(68.8)
TRS [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	165.8	587.5
Qualifying Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	952.5	817.9
Asset Fair Value	0.0	16.9
Liability Fair Value	(42.8)
Qualifying Hedges [Member] \| Net Investment Hedging [Member] \| Foreign Currency Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	952.5	817.9
Asset Fair Value	0.0	16.9
Liability Fair Value	(42.8)
Non-Qualifying Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	13,460.2	12,310.9
Asset Fair Value	79.4	94.7
Liability Fair Value	(72.2)	(68.8)
Non-Qualifying Hedges [Member] \| Foreign Currency Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,425.3	1,329.8
Asset Fair Value	16.6	30.2
Liability Fair Value	(27.5)	(6.0)
Non-Qualifying Hedges [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	6,335.7	5,309.2
Asset Fair Value	61.6	63.0
Liability Fair Value	(31.2)	(50.1)
Non-Qualifying Hedges [Member] \| Interest Rate Option [Member] \| Written options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,732.7	2,626.5
Asset Fair Value		0.1
Liability Fair Value	(0.8)	(1.0)
Non-Qualifying Hedges [Member] \| Interest Rate Option [Member] \| Purchased options [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,518.4	2,129.6
Asset Fair Value	0.8	1.0
Liability Fair Value		(0.1)
Non-Qualifying Hedges [Member] \| TRS [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	165.8	587.5
Liability Fair Value	(12.6)	(11.3)
Non-Qualifying Hedges [Member] \| Equity Warrants [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1.0	1.0
Asset Fair Value	0.3	0.2
Non-Qualifying Hedges [Member] \| Interest Rate Lock Commitments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	6.9	20.7
Asset Fair Value	0.1	0.1
Liability Fair Value		(0.1)
Non-Qualifying Hedges [Member] \| Forward Sale Commitments On Agency MBS [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	9.0	39.0
Asset Fair Value		0.1
Liability Fair Value	0.0
Non-Qualifying Hedges [Member] \| Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	265.4	267.6
Liability Fair Value	$ (0.1)	$ (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
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-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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-Name Accounting Standards Codification
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