Segment Reporting - Total Segments to Partnership Income Before Provision for Taxes Reconciliation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 1,034.6	$ 768.6	$ 1,419.9	$ 2,916.7
Costs and Expenses	643.4	505.3	1,498.1	1,636.1
Other income	23.9	(1.9)	(38.9)	(6.9)
Distributable earnings	415.1	261.4	(117.1)	1,273.7
Total assets	14,202.2		14,202.2		$ 13,808.8
Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues	496.5	527.8	1,659.8	1,529.4
Costs and Expenses	344.7	367.1	1,134.6	1,054.5
Other income	0.0	0.0	0.0	0.0
Distributable earnings	151.8	160.7	525.2	474.9
Total assets	8,460.6		8,460.6
Consolidated Funds
Segment Reporting Information [Line Items]
Revenues			164.5	149.5
Costs and Expenses			148.8	124.6
Other income			(38.9)	(6.9)
Distributable earnings	32.3	5.3	(23.2)	18.0
Total assets	5,893.1		5,893.1
Reconciling Items
Segment Reporting Information [Line Items]
Revenues	481.8	189.5	(404.4)	1,237.8
Costs and Expenses	250.8	94.1	214.7	457.0
Other income	0.0	0.0	0.0	0.0
Distributable earnings	231.0	$ 95.4	(619.1)	$ 780.8
Total assets	$ (151.5)		$ (151.5)