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Intangible Assets - Schedule of Changes in the Components of Acquired Client Relationships (Details) $ in Millions		6 Months Ended
		Jun. 30, 2015 USD ($)
Indefinite-lived
Beginning balance, net		$ 1,088.3
New investments	[1]	0.0
Amortization and impairments		0.0
Foreign currency translation		3.8
Ending balance, net		1,092.1
Total
Beginning balance, net		1,778.4
New investments	[1]	23.6
Amortization and impairments		(55.9)
Foreign currency translation		3.7
Ending balance, net		1,749.8
Acquired Client Relationships
Definite-lived
Beginning balance, gross		1,255.1
Beginning balance, accumulated amortization		(565.0)
Beginning balance, net		690.1
New investments	[1]	23.6
Amortization and impairments		(55.9)
Foreign currency translation		(0.1)
Ending balance, gross		1,278.6
Ending balance, accumulated amortization		(620.9)
Ending balance, net		$ 657.7
[1] On April 1, 2015, the Company completed its investment in Baker Street Advisors, LLC.

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