Segment Reporting - Reportable Segments Financial Data (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Fund level fee revenues
Fund management fees	$ 242.2	$ 239.9	$ 473.6	$ 474.3
Performance fees
Realized	203.2	116.7	456.0	397.3
Unrealized	55.9	(337.1)	445.5	23.1
Total performance fees	259.1	(220.4)	901.5	420.4
Compensation and benefits
Equity-based compensation	4.2	0.6	6.8	0.6
Performance fee related
Total compensation and benefits	443.7	178.5	978.2	373.7
Economic Net Income	155.8	(57.2)	549.7	334.9
(-) Net Performance Fees	122.5	(106.7)	477.2	228.1
(-) Investment Income	11.0	7.0	11.4	28.5
(=) Fee Related Earnings	26.4	35.5	62.6	69.5
(+) Realized Investment Income	12.7	2.4	8.5	1.6
(+) Equity-based compensation	4.2	0.6	6.8	0.6
Segment assets as of June 30, 2013	33,787.2		33,787.2		31,566.6
Corporate Private Equity [Member]
Performance fees
Total performance fees	186.2	(217.6)	620.9	246.9
Global Market Strategies [Member]
Performance fees
Total performance fees	48.7	6.9	157.2	52.4
Real Assets [Member]
Performance fees
Total performance fees	(13.9)	(30.4)	49.1	75.1
Total Reportable Segments [Member]
Fund level fee revenues
Fund management fees	249.9	235.0	490.0	460.4
Portfolio advisory fees, net	5.7	7.0	10.3	15.0
Transaction fees, net	6.8	3.7	17.2	6.4
Total fee revenues	262.4	245.7	517.5	481.8
Performance fees
Realized	192.6	110.3	441.5	392.1
Unrealized	42.1	(311.1)	384.8	38.6
Total performance fees	234.7	(200.8)	826.3	430.7
Investment income (loss)
Realized	14.6	4.0	5.3	6.1
Unrealized	(7.7)	10.0	4.6	31.2
Total investment income	6.9	14.0	9.9	37.3
Interest and other income	4.0	2.5	6.4	5.1
Total revenues	508.0	61.4	1,360.1	954.9
Compensation and benefits
Direct base compensation	101.0	105.8	209.0	207.0
Indirect base compensation	35.0	36.2	68.6	69.3
Equity-based compensation	4.2	0.6	6.8	0.6
Performance fee related
Realized	74.8	34.5	182.2	173.6
Unrealized	37.4	(128.6)	166.9	29.0
Total compensation and benefits	252.4	48.5	633.5	479.5
General, administrative, and other indirect expenses	82.0	60.0	144.3	115.4
Depreciation and amortization expense	6.2	4.0	12.5	9.2
Interest expense	11.6	6.1	20.1	15.9
Total expenses	352.2	118.6	810.4	620.0
Economic Net Income	155.8	(57.2)	549.7	334.9
(-) Net Performance Fees	122.5	(106.7)	477.2	228.1
(-) Investment Income	6.9	14.0	9.9	37.3
(=) Fee Related Earnings	26.4	35.5	62.6	69.5
(+) Realized Net Performance Fees	117.8	75.8	259.3	218.5
(+) Realized Investment Income	14.6	4.0	5.3	6.1
(+) Equity-based compensation	4.2	0.6	6.8	0.6
(=) Distributable Earnings	163.0	115.9	334.0	294.7
Segment assets as of June 30, 2013	5,175.2		5,175.2
Total Reportable Segments [Member] | Corporate Private Equity [Member]
Fund level fee revenues
Fund management fees	108.8	124.0	217.1	247.9
Portfolio advisory fees, net	4.9	4.9	9.0	11.9
Transaction fees, net	4.0	1.6	14.4	3.2
Total fee revenues	117.7	130.5	240.5	263.0
Performance fees
Realized	151.4	80.6	363.7	303.6
Unrealized	31.2	(269.7)	238.8	(28.4)
Total performance fees	182.6	(189.1)	602.5	275.2
Investment income (loss)
Realized	1.7	1.5	3.5	2.3
Unrealized	2.4	3.7	5.2	18.2
Total investment income	4.1	5.2	8.7	20.5
Interest and other income	1.7	1.6	2.7	3.0
Total revenues	306.1	(51.8)	854.4	561.7
Compensation and benefits
Direct base compensation	50.0	54.8	105.0	110.1
Indirect base compensation	21.8	24.1	41.8	44.9
Equity-based compensation	2.3	0.4	3.8	0.4
Performance fee related
Realized	65.1	31.0	166.7	148.6
Unrealized	8.8	(140.3)	92.4	(8.3)
Total compensation and benefits	148.0	(30.0)	409.7	295.7
General, administrative, and other indirect expenses	41.6	36.9	80.6	71.7
Depreciation and amortization expense	3.4	2.3	6.9	5.5
Interest expense	6.7	3.5	11.6	9.4
Total expenses	199.7	12.7	508.8	382.3
Economic Net Income	106.4	(64.5)	345.6	179.4
(-) Net Performance Fees	108.7	(79.8)	343.4	134.9
(-) Investment Income	4.1	5.2	8.7	20.5
(=) Fee Related Earnings	(6.4)	10.1	(6.5)	24.0
(+) Realized Net Performance Fees	86.3	49.6	197.0	155.0
(+) Realized Investment Income	1.7	1.5	3.5	2.3
(+) Equity-based compensation	2.3	0.4	3.8	0.4
(=) Distributable Earnings	83.9	61.6	197.8	181.7
Segment assets as of June 30, 2013	2,693.2		2,693.2
Total Reportable Segments [Member] | Global Market Strategies [Member]
Fund level fee revenues
Fund management fees	73.8	59.5	140.1	108.1
Portfolio advisory fees, net	0.5	0.5	0.7	1.2
Transaction fees, net	0.1		0.1
Total fee revenues	74.4	60.0	140.9	109.3
Performance fees
Realized	17.9	1.3	42.0	33.7
Unrealized	23.0	4.0	87.3	16.7
Total performance fees	40.9	5.3	129.3	50.4
Investment income (loss)
Realized	12.2	2.8	14.1	4.1
Unrealized	(11.9)	4.8	(6.8)	8.5
Total investment income	0.3	7.6	7.3	12.6
Interest and other income	1.5	0.4	2.6	1.0
Total revenues	117.1	73.3	280.1	173.3
Compensation and benefits
Direct base compensation	24.9	25.2	50.6	44.9
Indirect base compensation	5.5	4.5	10.3	9.4
Equity-based compensation	0.6	0.1	1.0	0.1
Performance fee related
Realized	6.7	0.7	16.4	18.5
Unrealized	9.6	0.2	15.8	9.9
Total compensation and benefits	47.3	30.7	94.1	82.8
General, administrative, and other indirect expenses	19.5	9.1	29.0	16.4
Depreciation and amortization expense	1.1	0.6	2.3	1.4
Interest expense	2.1	0.9	3.6	2.6
Total expenses	70.0	41.3	129.0	103.2
Economic Net Income	47.1	32.0	151.1	70.1
(-) Net Performance Fees	24.6	4.4	97.1	22.0
(-) Investment Income	0.3	7.6	7.3	12.6
(=) Fee Related Earnings	22.2	20.0	46.7	35.5
(+) Realized Net Performance Fees	11.2	0.6	25.6	15.2
(+) Realized Investment Income	12.2	2.8	14.1	4.1
(+) Equity-based compensation	0.6	0.1	1.0	0.1
(=) Distributable Earnings	46.2	23.5	87.4	54.9
Segment assets as of June 30, 2013	1,102.3		1,102.3
Total Reportable Segments [Member] | Real Assets [Member]
Fund level fee revenues
Fund management fees	46.4	34.1	93.4	70.7
Portfolio advisory fees, net	0.3	1.6	0.6	1.9
Transaction fees, net	2.7	2.1	2.7	3.2
Total fee revenues	49.4	37.8	96.7	75.8
Performance fees
Realized	20.6	27.0	31.6	50.2
Unrealized	(33.4)	(56.0)	16.1	26.4
Total performance fees	(12.8)	(29.0)	47.7	76.6
Investment income (loss)
Realized	0.7	(0.3)	(12.3)	(0.3)
Unrealized	1.7	1.5	6.2	4.5
Total investment income	2.4	1.2	(6.1)	4.2
Interest and other income	0.6	0.4	0.9	0.8
Total revenues	39.6	10.4	139.2	157.4
Compensation and benefits
Direct base compensation	18.2	16.9	36.1	35.1
Indirect base compensation	6.4	5.6	13.9	12.0
Equity-based compensation	1.2	0.1	1.8	0.1
Performance fee related
Realized	1.6	1.5	(3.3)	2.4
Unrealized	2.9	2.1	26.5	8.0
Total compensation and benefits	30.3	26.2	75.0	57.6
General, administrative, and other indirect expenses	16.5	11.1	26.9	22.8
Depreciation and amortization expense	1.2	0.7	2.3	1.7
Interest expense	2.2	1.1	3.8	3.0
Total expenses	50.2	39.1	108.0	85.1
Economic Net Income	(10.6)	(28.7)	31.2	72.3
(-) Net Performance Fees	(17.3)	(32.6)	24.5	66.2
(-) Investment Income	2.4	1.2	(6.1)	4.2
(=) Fee Related Earnings	4.3	2.7	12.8	1.9
(+) Realized Net Performance Fees	19.0	25.5	34.9	47.8
(+) Realized Investment Income	0.7	(0.3)	(12.3)	(0.3)
(+) Equity-based compensation	1.2	0.1	1.8	0.1
(=) Distributable Earnings	25.2	28.0	37.2	49.5
Segment assets as of June 30, 2013	953.6		953.6
Total Reportable Segments [Member] | Global Solutions [Member]
Fund level fee revenues
Fund management fees	20.9	17.4	39.4	33.7
Total fee revenues	20.9	17.4	39.4	33.7
Performance fees
Realized	2.7	1.4	4.2	4.6
Unrealized	21.3	10.6	42.6	23.9
Total performance fees	24.0	12.0	46.8	28.5
Investment income (loss)
Unrealized	0.1
Total investment income	0.1
Interest and other income	0.2	0.1	0.2	0.3
Total revenues	45.2	29.5	86.4	62.5
Compensation and benefits
Direct base compensation	7.9	8.9	17.3	16.9
Indirect base compensation	1.3	2.0	2.6	3.0
Equity-based compensation	0.1		0.2
Performance fee related
Realized	1.4	1.3	2.4	4.1
Unrealized	16.1	9.4	32.2	19.4
Total compensation and benefits	26.8	21.6	54.7	43.4
General, administrative, and other indirect expenses	4.4	2.9	7.8	4.5
Depreciation and amortization expense	0.5	0.4	1.0	0.6
Interest expense	0.6	0.6	1.1	0.9
Total expenses	32.3	25.5	64.6	49.4
Economic Net Income	12.9	4.0	21.8	13.1
(-) Net Performance Fees	6.5	1.3	12.2	5.0
(-) Investment Income	0.1
(=) Fee Related Earnings	6.3	2.7	9.6	8.1
(+) Realized Net Performance Fees	1.3	0.1	1.8	0.5
(+) Equity-based compensation	0.1		0.2
(=) Distributable Earnings	7.7	2.8	11.6	8.6
Segment assets as of June 30, 2013	$ 426.1		$ 426.1