Investments - Schedule of Net Investment Earnings (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Management fees	$ 21.3	$ 20.9	$ 58.9	$ 62.1
Performance fees	7.4	37.9	62.7	47.6
Investment income	1.6	6.4	7.8	10.8
Expenses	(10.6)	(4.1)	(46.2)	(10.7)
Amortization of basis differences	(2.1)	(13.8)	(6.4)	(41.4)
Net investment income	$ 17.6	$ 47.3	$ 76.8	$ 68.4

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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