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Intangible Assets - Schedule of Changes in the Components of Acquired Client Relationships (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)
Indefinite-lived
Beginning balance, net	$ 1,088.3
New investments	0.0	[1]
Amortization and impairments	0.0
Foreign currency translation	(12.3)
Ending balance, net	1,076.0
Total
Beginning balance, net	1,778.4
New investments	23.6	[1]
Amortization and impairments	(86.4)
Foreign currency translation	(15.9)
Ending balance, net	1,699.7
Acquired Client Relationships
Definite-lived
Beginning balance, gross	1,255.1
Beginning balance, accumulated amortization	(565.0)
Beginning balance, net	690.1
New investments	23.6	[1]
Amortization and impairments	(86.4)
Foreign currency translation	(3.6)
Ending balance, gross	1,275.1
Ending balance, accumulated amortization	(651.4)
Ending balance, net	$ 623.7
[1] On April 1, 2015, the Company completed its investment in Baker Street Advisors, LLC.

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