Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2016	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to partners’ capital	$ 2,949.0	$ 1,454.0	$ 6,077.6		$ 9,094.5
Accrued performance fee-related compensation	$ 1,894.8	1,307.4
Percentage of estimated realizable tax benefit to be paid by corporate taxpayers on exchange transactions	85.00%
Percentage of remaining estimated realizable tax benefit on exchange transactions	15.00%
Foreign currency transaction (gain) losses before tax	$ (3.9)	$ (26.3)	$ 2.5
Percentage of performance fees to be accounted for as earnings of financial assets	90.00%	90.00%	90.00%
Accounting Standards Update 2014-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to partners’ capital				$ 2.0