Intangible Assets (Schedule of finite-lived intangible assets by major class) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Gross Book Value	$ 1,325.5	$ 1,349.9
Accumulated Amortization	(78.8)	(86.2)
Net Book Value	1,246.7us-gaap_FiniteLivedIntangibleAssetsNet	1,263.7us-gaap_FiniteLivedIntangibleAssetsNet
Management contracts - indefinite-lived [Member]
Indefinite-Lived Intangible Assets (Excluding Goodwill)	1,195.9	1,200.0
Management contracts - finite-lived [Member]
Gross Book Value	88.8	92.1
Accumulated Amortization	(62.9)	(58.5)
Net Book Value	25.9	33.6
Weighted Average Amortization Period (years)	3 years 6 months	3 years 6 months
Customer relationships [Member]
Gross Book Value	40.0	40.0
Accumulated Amortization	(15.2)	(11.9)
Net Book Value	24.8	28.1
Weighted Average Amortization Period (years)	8 years 5 months	8 years 5 months
Distribution agreements [Member]
Gross Book Value		17.0
Accumulated Amortization		(15.2)
Net Book Value		1.8
Weighted Average Amortization Period (years)		4 years 0 months
Other [Member]
Gross Book Value	0.8	0.8
Accumulated Amortization	(0.7)	(0.6)
Net Book Value	$ 0.1	$ 0.2
Weighted Average Amortization Period (years)	2 years 10 months	2 years 10 months

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275

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- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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