Segment Reporting - Reportable Segments Financial Data (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
Fund level fee revenues
Investment income (loss)	$ 584.1	$ 324.6	$ 72.4	$ 1,565.1
Interest income	21.3	23.3	64.5	71.5
Total revenues	1,034.6	768.6	1,419.9	2,916.7
Compensation and benefits
Cash-based compensation and benefits	222.2	200.0	639.0	631.9
Realized performance revenues related compensation	250.6	92.6	343.7	391.6
Total compensation and benefits	491.5	329.2	1,061.0	1,131.3
General, administrative and other expenses	91.1	121.7	240.9	344.9
Interest	23.0	20.0	72.8	59.2
Total expenses	643.4	505.3	1,498.1	1,636.1
Realized net performance revenues	226.8	19.8	387.9	317.5
Segment assets	14,202.2		14,202.2		$ 13,808.8
Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues	394.2	395.7	1,187.2	1,216.7
Interest income	2.7	6.5	11.2	18.0
Total revenues	496.5	527.8	1,659.8	1,529.4
Compensation and benefits
Cash-based compensation and benefits	205.3	194.1	619.2	603.5
Realized performance revenues related compensation	46.9	60.6	251.6	123.9
Total compensation and benefits	252.2	254.7	870.8	727.4
General, administrative and other expenses	62.0	81.0	168.4	236.7
Depreciation and amortization expense	8.2	11.8	24.8	31.7
Interest	22.3	19.6	70.6	58.7
Total expenses	344.7	367.1	1,134.6	1,054.5
Distributable Earnings	151.8	160.7	525.2	474.9
Realized net performance revenues	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
Segment assets	8,460.6		8,460.6
Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues	183.9	200.9	566.8	596.0
Interest income	0.2	1.7	1.7	4.1
Total revenues	247.4	237.7	750.3	668.5
Compensation and benefits
Cash-based compensation and benefits	91.2	92.6	280.2	290.4
Realized performance revenues related compensation	27.0	14.9	69.5	30.7
Total compensation and benefits	118.2	107.5	349.7	321.1
General, administrative and other expenses	28.2	34.8	68.4	102.2
Depreciation and amortization expense	3.8	5.7	11.6	15.1
Interest	9.7	8.0	29.9	23.8
Total expenses	159.9	156.0	459.6	462.2
Distributable Earnings	87.5	81.7	290.7	206.3
Realized net performance revenues	31.3	18.4	82.9	37.2
Realized principal investment income (loss)	5.0	1.8	29.4	0.5
Net Interest	9.5	6.3	28.2	19.7
Fee Related Earnings	60.7	67.8	206.6	188.3
Segment assets	4,221.0		4,221.0
Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues	67.7	78.0	223.3	265.0
Interest income	0.1	0.8	0.9	2.0
Total revenues	82.5	147.7	328.1	437.1
Compensation and benefits
Cash-based compensation and benefits	31.3	33.1	102.6	102.9
Realized performance revenues related compensation	5.9	29.2	44.9	52.4
Total compensation and benefits	37.2	62.3	147.5	155.3
General, administrative and other expenses	12.2	16.7	46.8	50.5
Depreciation and amortization expense	1.5	2.2	4.6	5.9
Interest	4.0	3.2	13.5	9.4
Total expenses	54.9	84.4	212.4	221.1
Distributable Earnings	27.6	63.3	115.7	216.0
Realized net performance revenues	6.3	35.8	54.4	42.1
Realized principal investment income (loss)	2.5	3.9	4.6	75.6
Net Interest	3.9	2.4	12.6	7.4
Fee Related Earnings	22.7	26.0	69.3	105.7
Segment assets	1,348.4		1,348.4
Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues	87.8	78.1	256.9	238.4
Interest income	2.3	3.6	8.0	10.8
Total revenues	94.6	84.8	306.3	258.4
Compensation and benefits
Cash-based compensation and benefits	52.5	43.9	156.1	140.0
Realized performance revenues related compensation	0.0	0.0	12.2	0.0
Total compensation and benefits	52.5	43.9	168.3	140.0
General, administrative and other expenses	12.0	20.9	30.7	57.9
Depreciation and amortization expense	1.8	2.4	5.2	6.5
Interest	6.3	6.5	20.2	19.9
Total expenses	72.6	73.7	224.4	224.3
Distributable Earnings	22.0	11.1	81.9	34.1
Realized net performance revenues	0.0	0.9	14.3	1.0
Realized principal investment income (loss)	4.5	2.2	14.9	8.2
Net Interest	4.0	2.9	12.2	9.1
Fee Related Earnings	21.5	10.9	64.9	34.0
Segment assets	1,800.1		1,800.1
Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues	54.8	38.7	140.2	117.3
Interest income	0.1	0.4	0.6	1.1
Total revenues	72.0	57.6	275.1	165.4
Compensation and benefits
Cash-based compensation and benefits	30.3	24.5	80.3	70.2
Realized performance revenues related compensation	14.0	16.5	125.0	40.8
Total compensation and benefits	44.3	41.0	205.3	111.0
General, administrative and other expenses	9.6	8.6	22.5	26.1
Depreciation and amortization expense	1.1	1.5	3.4	4.2
Interest	2.3	1.9	7.0	5.6
Total expenses	57.3	53.0	238.2	146.9
Distributable Earnings	14.7	4.6	36.9	18.5
Realized net performance revenues	2.3	2.6	7.4	5.2
Realized principal investment income (loss)	0.8	(0.6)	1.9	1.0
Net Interest	2.2	1.5	6.4	4.5
Fee Related Earnings	13.8	4.1	34.0	16.8
Segment assets	1,091.1		1,091.1
Fund management fees
Fund level fee revenues
Total fund level fee revenues	363.8	359.5	1,091.5	1,103.8
Fund management fees | Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues	389.1	384.6	1,157.0	1,180.7
Fund management fees | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues	180.7	192.2	556.9	572.5
Fund management fees | Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues	67.4	78.1	222.4	261.3
Fund management fees | Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues	86.2	75.6	237.5	229.6
Fund management fees | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues	54.8	38.7	140.2	117.3
Portfolio advisory fees, net and other | Total Reportable Segments
Fund level fee revenues
Total fund level fee revenues	5.1	11.1	30.2	36.0
Portfolio advisory fees, net and other | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Total fund level fee revenues	3.2	8.7	9.9	23.5
Portfolio advisory fees, net and other | Total Reportable Segments | Real Assets
Fund level fee revenues
Total fund level fee revenues	0.3	(0.1)	0.9	3.7
Portfolio advisory fees, net and other | Total Reportable Segments | Global Credit
Fund level fee revenues
Total fund level fee revenues	1.6	2.5	19.4	8.8
Portfolio advisory fees, net and other | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Total fund level fee revenues	0.0	0.0	0.0	0.0
Performance allocations
Fund level fee revenues
Investment income (loss)	477.4	112.4	731.6	709.1
Performance allocations | Total Reportable Segments
Fund level fee revenues
Investment income (loss)	86.8	118.3	410.6	209.4
Performance allocations | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Investment income (loss)	58.3	33.3	152.4	67.9
Performance allocations | Total Reportable Segments | Real Assets
Fund level fee revenues
Investment income (loss)	12.2	65.0	99.3	94.5
Performance allocations | Total Reportable Segments | Global Credit
Fund level fee revenues
Investment income (loss)	0.0	0.9	26.5	1.0
Performance allocations | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Investment income (loss)	16.3	19.1	132.4	46.0
Principal investment income (loss)
Fund level fee revenues
Investment income (loss)	106.7	212.2	(659.2)	856.0
Principal investment income (loss) | Total Reportable Segments
Fund level fee revenues
Investment income (loss)	12.8	7.3	50.8	85.3
Principal investment income (loss) | Total Reportable Segments | Corporate Private Equity
Fund level fee revenues
Investment income (loss)	5.0	1.8	29.4	0.5
Principal investment income (loss) | Total Reportable Segments | Real Assets
Fund level fee revenues
Investment income (loss)	2.5	3.9	4.6	75.6
Principal investment income (loss) | Total Reportable Segments | Global Credit
Fund level fee revenues
Investment income (loss)	4.5	2.2	14.9	8.2
Principal investment income (loss) | Total Reportable Segments | Investment Solutions
Fund level fee revenues
Investment income (loss)	$ 0.8	$ (0.6)	$ 1.9	$ 1.0