Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	$ 22.0	$ 28.6	$ 43.9	$ 55.3
Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Weighted average client-acquired relationships			12 years
Finite-lived intangible, future amortization expense, next twelve months	85.0		$ 85.0
Finite-lived intangible, future amortization expense, year 2	85.0		85.0
Finite-lived intangible, future amortization expense, year 3	85.0		85.0
Finite-lived intangible, future amortization expense, year 4	50.0		50.0
Finite-lived intangible, future amortization expense, year 5	30.0		30.0
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Revenue from equity method investments	259.2	222.4	524.8	428.5
Net income from equity method investments	144.4	122.9	$ 293.0	234.6
Equity Method Investee | Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Weighted average client-acquired relationships			13 years
Amortization expense during the period	24.0	14.8	$ 45.8	29.0
Finite-lived intangible, future amortization expense, next twelve months	85.0		85.0
Finite-lived intangible, future amortization expense, year 2	85.0		85.0
Finite-lived intangible, future amortization expense, year 3	85.0		85.0
Finite-lived intangible, future amortization expense, year 4	85.0		85.0
Finite-lived intangible, future amortization expense, year 5	85.0		85.0
Systematica Investment LP and Baring Private Equity Asia | Equity Method Investee | Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	$ 3.7	$ 4.5	$ 7.4	$ 7.4