Segment Reporting - Reportable Segments Financial Data (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fund level fee revenues
Incentive fees and Investment income (loss)									$ 1,568.4	$ 809.2	$ 2,290.6
Interest income									97.3	101.3	36.7
Total revenues	$ 460.3	$ 768.6	$ 1,061.1	$ 1,087.0	$ 151.7	$ 679.1	$ 893.6	$ 702.8	3,377.0	2,427.2	3,676.2
Compensation and benefits
Cash-based compensation and benefits									833.4	746.7	652.7
Realized performance revenues related compensation									436.7	376.3	988.3
Total compensation and benefits									1,410.1	1,362.9	1,961.3
General, administrative and other expenses									494.4	460.7	276.8
Interest expense									82.1	82.2	65.5
Total expenses	483.6	$ 505.3	$ 528.3	$ 602.5	222.9	$ 615.6	$ 653.7	$ 579.3	2,119.7	2,071.5	2,632.3
Segment assets	13,808.8				12,914.2				13,808.8	12,914.2	12,280.6
Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues									1,624.4	1,425.0	1,140.0
Interest income									24.4	30.4	16.7
Total revenues									2,110.1	2,185.9	2,216.2
Compensation and benefits
Cash-based compensation and benefits									792.1	740.7	658.0
Total compensation and benefits									1,002.3	1,103.4	1,190.7
General, administrative and other expenses									331.3	298.8	258.9
Depreciation and amortization expense									48.2	35.1	31.1
Interest expense									81.7	74.7	65.5
Total expenses									1,463.5	1,512.0	1,546.2
Distributable Earnings									646.6	673.9	670.0
Realized principal investment income (loss)									87.0	48.1	(25.8)
Net interest									57.3	44.3	48.8
Fee Related Earnings									452.8	350.4	192.0
Segment assets	8,787.9				7,470.7				8,787.9	7,470.7
Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues									796.3	681.9	514.6
Interest income									6.0	9.3	5.5
Total revenues									920.7	1,133.7	1,377.0
Compensation and benefits
Cash-based compensation and benefits									371.7	373.2	340.7
Total compensation and benefits									426.4	568.5	713.6
General, administrative and other expenses									140.8	167.6	132.3
Depreciation and amortization expense									23.1	17.3	15.3
Interest expense									33.6	29.9	27.9
Total expenses									623.9	783.3	889.1
Distributable Earnings									296.8	350.4	487.9
Realized principal investment income (loss)									(3.3)	26.6	25.4
Net interest									27.6	20.6	22.4
Fee Related Earnings									260.7	123.8	26.3
Segment assets	3,226.1				2,980.0				3,226.1	2,980.0
Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues									349.2	326.8	271.1
Interest income									2.7	4.4	3.0
Total revenues									608.6	495.0	302.9
Compensation and benefits
Cash-based compensation and benefits									138.9	135.1	128.1
Total compensation and benefits									229.4	201.7	169.7
General, administrative and other expenses									74.4	64.1	84.3
Depreciation and amortization expense									9.0	6.8	7.1
Interest expense									13.2	15.3	17.0
Total expenses									326.0	287.9	278.1
Distributable Earnings									282.6	207.1	24.8
Realized principal investment income (loss)									76.6	13.5	(63.2)
Net interest									10.5	10.9	14.0
Fee Related Earnings									126.9	120.8	51.6
Segment assets	1,770.9				1,738.8				1,770.9	1,738.8
Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues									321.8	249.1	199.0
Interest income									14.2	15.3	7.1
Total revenues									349.8	282.1	293.4
Compensation and benefits
Cash-based compensation and benefits									185.2	140.4	104.5
Total compensation and benefits									185.6	144.9	139.5
General, administrative and other expenses									78.9	30.5	7.4
Depreciation and amortization expense									9.9	6.3	5.1
Interest expense									27.0	22.9	14.5
Total expenses									301.4	204.6	166.5
Distributable Earnings									48.4	77.5	126.9
Realized principal investment income (loss)									12.0	7.9	11.9
Net interest									12.8	7.6	7.4
Fee Related Earnings									47.8	71.9	82.0
Segment assets	2,564.7				1,702.9				2,564.7	1,702.9
Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues									157.1	167.2	155.3
Interest income									1.5	1.4	1.1
Total revenues									231.0	275.1	242.9
Compensation and benefits
Cash-based compensation and benefits									96.3	92.0	84.7
Total compensation and benefits									160.9	188.3	167.9
General, administrative and other expenses									37.2	36.6	34.9
Depreciation and amortization expense									6.2	4.7	3.6
Interest expense									7.9	6.6	6.1
Total expenses									212.2	236.2	212.5
Distributable Earnings									18.8	38.9	30.4
Realized principal investment income (loss)									1.7	0.1	0.1
Net interest									6.4	5.2	5.0
Fee Related Earnings									17.4	33.9	32.1
Segment assets	$ 1,226.2				$ 1,049.0				1,226.2	1,049.0
Fund management fees
Fund level fee revenues
Total fund level fee revenues									1,476.2	1,272.0	1,026.9
Fund management fees | Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues									1,570.9	1,361.8	1,081.0
Fund management fees | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues									767.8	634.1	471.0
Fund management fees | Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues									338.8	317.9	263.6
Fund management fees | Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues									307.2	243.0	191.5
Fund management fees | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues									157.1	166.8	154.9
Portfolio advisory fees, net and other | Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues									22.2	31.1	32.1
Portfolio advisory fees, net and other | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues									15.8	21.1	21.2
Portfolio advisory fees, net and other | Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues									1.7	4.5	3.0
Portfolio advisory fees, net and other | Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues									4.7	5.1	7.5
Portfolio advisory fees, net and other | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues									0.0	0.4	0.4
Transaction fees, net | Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues									31.3	32.1	26.9
Transaction fees, net | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues									12.7	26.7	22.4
Transaction fees, net | Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues									8.7	4.4	4.5
Transaction fees, net | Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues									9.9	1.0	0.0
Transaction fees, net | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues									0.0	0.0	0.0
Performance allocations
Fund level fee revenues
Incentive fees and Investment income (loss)									799.1	622.9	2,058.6
Compensation and benefits
Realized performance revenues related compensation									436.7	376.3	988.3
Realized net performance revenues									362.4	246.6	1,070.3
Performance allocations | Total Reportable Segments
Fund level fee revenues
Incentive fees and Investment income (loss)									374.3	682.4	1,085.3
Compensation and benefits
Realized performance revenues related compensation									210.2	362.7	532.7
Realized net performance revenues									164.1	319.7	552.6
Performance allocations | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Incentive fees and Investment income (loss)									121.7	415.9	831.5
Compensation and benefits
Realized performance revenues related compensation									54.7	195.3	372.9
Realized net performance revenues									67.0	220.6	458.6
Performance allocations | Total Reportable Segments | Real Assets
Fund level fee revenues
Incentive fees and Investment income (loss)									180.1	150.3	92.0
Compensation and benefits
Realized performance revenues related compensation									90.5	66.6	41.6
Realized net performance revenues									89.6	83.7	50.4
Performance allocations | Total Reportable Segments | Global Credit
Fund level fee revenues
Incentive fees and Investment income (loss)									1.8	9.8	75.4
Compensation and benefits
Realized performance revenues related compensation									0.4	4.5	35.0
Realized net performance revenues									1.4	5.3	40.4
Performance allocations | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Incentive fees and Investment income (loss)									70.7	106.4	86.4
Compensation and benefits
Realized performance revenues related compensation									64.6	96.3	83.2
Realized net performance revenues									6.1	10.1	3.2
Realized principal investment income (loss)
Fund level fee revenues
Incentive fees and Investment income (loss)									769.3	186.3	232.0
Realized principal investment income (loss) | Total Reportable Segments
Fund level fee revenues
Incentive fees and Investment income (loss)									87.0	48.1	(25.8)
Realized principal investment income (loss) | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Incentive fees and Investment income (loss)									(3.3)	26.6	25.4
Realized principal investment income (loss) | Total Reportable Segments | Real Assets
Fund level fee revenues
Incentive fees and Investment income (loss)									76.6	13.5	(63.2)
Realized principal investment income (loss) | Total Reportable Segments | Global Credit
Fund level fee revenues
Incentive fees and Investment income (loss)									12.0	7.9	11.9
Realized principal investment income (loss) | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Incentive fees and Investment income (loss)									$ 1.7	$ 0.1	$ 0.1