Fair Value Measurements - Schedule of Level Three Investment Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Consolidated Funds other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
At beginning of the period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Transfers in (out) of Level 3	0.0		0.0	26.5
Change in recognition based on adoption of ASU 2016-01	0.0	0.0	0.0	0.0
Total net fair value losses recognized in net income	0.0	0.0	0.0	0.0
Total Level III financial assets	0.0	26.5	0.0	26.5
Investments in unconsolidated Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
At beginning of the period	3.0	6.3	3.0	0.0
Transfers in (out) of Level 3		0.0	0.0	0.0
Change in recognition based on adoption of ASU 2016-01	0.0	0.0	0.0	6.4
Total net fair value losses recognized in net income	0.0	(1.1)	0.0	(1.2)
Total Level III financial assets	$ 3.0	$ 5.2	$ 3.0	$ 5.2

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Deconsolidation Of Funds

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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