Segment Reporting - Total Segments to Partnership Income Before Provision for Taxes Reconciliation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,639.5	$ 1,034.6	$ 6,783.0	$ 1,419.9
Expenses	938.1	643.4	3,674.3	1,498.1
Other income (loss)	(0.1)	23.9	9.6	(38.9)
Distributable earnings	701.3	415.1	3,118.3	(117.1)
Consolidated VIEs, assets	20,788.7		20,788.7		$ 15,644.8
Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues	1,523.8	496.5	3,055.3	1,659.8
Expenses	793.2	344.7	1,714.4	1,134.6
Other income (loss)	0.0	0.0	0.0	0.0
Distributable earnings	730.6	151.8	1,340.9	525.2
Consolidated VIEs, assets	14,190.7		14,190.7
Consolidated Funds
Segment Reporting Information [Line Items]
Revenues	62.1	56.3	185.3	164.5
Expenses	51.9	47.9	162.6	148.8
Other income (loss)	(0.1)	23.9	9.6	(38.9)
Distributable earnings	10.1	32.3	32.3	(23.2)
Consolidated VIEs, assets	6,778.2		6,778.2
Reconciling Items
Segment Reporting Information [Line Items]
Revenues	53.6	481.8	3,542.4	(404.4)
Expenses	93.0	250.8	1,797.3	214.7
Other income (loss)	0.0	0.0	0.0	0.0
Distributable earnings	(39.4)	$ 231.0	1,745.1	$ (619.1)
Consolidated VIEs, assets	$ (180.2)		$ (180.2)