Segment Reporting - Reconciliation of Income Before Provision for Income Taxes (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Income before provision for income taxes	$ 415.1	$ 261.4	$ (117.1)	$ 1,273.7
Adjustments:
Investment income (loss)	(584.1)	(324.6)	(72.4)	(1,565.1)
Equity-based compensation	18.7	36.6	78.3	107.8
Other non-operating (income) expense	0.6	0.3	1.3	1.0
Net income attributable to non-controlling interests in Consolidated entities	37.2	10.5	(1.2)	45.8
Realized performance revenues, net of related compensation	226.8	19.8	387.9	317.5
Total Reportable Segments
Adjustments:
Net unrealized performance revenues	(180.3)	126.2	(238.8)	(112.0)
Distributable Earnings	151.8	160.7	525.2	474.9
Realized performance revenues, net of related compensation	39.9	57.7	159.0	85.5
Realized principal investment income (loss)	12.8	7.3	50.8	85.3
Net Interest	19.6	13.1	59.4	40.7
Fee Related Earnings	118.7	108.8	374.8	344.8
Reconciling Items
Adjustments:
Equity-based compensation	21.1	38.9	87.4	116.6
Acquisition related charges and amortization of intangibles and impairment	18.5	11.2	28.6	38.6
Other non-operating (income) expense	0.6	0.3	1.3	1.0
Tax expense associated with performance revenues	(7.8)	(10.8)	4.1	(13.3)
Net income attributable to non-controlling interests in Consolidated entities	(37.2)	(10.5)	1.2	(45.8)
Debt extinguishment costs	0.0	0.0	0.0	0.1
Severance and other adjustments	2.8	10.8	10.9	23.4
Unrealized principal investment income (loss) | Reconciling Items
Adjustments:
Investment income (loss)	(81.0)	(198.7)	643.2	(672.2)
Unrealized principal investment income (loss) | Reconciling Items | Fortitude Group Holdings, LLC
Adjustments:
Investment income (loss)	$ 0.0	$ (68.1)	$ 104.4	$ (135.2)