Summary of Significant Accounting Policies - Accounting Pronouncements (Details) - USD ($) $ in Millions	Jan. 01, 2018	Jan. 01, 2019
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment, net of tax	$ 35.0
Carried interest distributions	77.9
Revenue sharing expense	$ 42.7
Minimum | Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 430.0
Operating lease, liability		560.0
Maximum | Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		440.0
Operating lease, liability		$ 570.0