Segment Reporting - Reportable Segments Financial Data (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Performance fee related
Depreciation and amortization expense	$ 22.2	$ 22.2	$ 20.9
Economic Net Income	735.6	833.1	1,014.0
Fee Related Earnings	169.5	121.3	198.6
Net performance fees	524.6	630.4	743.8
Distributable Earnings	$ 687.9	$ 864.4	$ 342.5
Corporate Private Equity [Member]
Fund level fee revenues
Fund management fees	496.2	511.3	537.6
Portfolio advisory fees, net	17.8	31.3	14.9
Transaction fees, net	19.0	34.7	21.5
Total fund level fee revenues	533.0	577.3	574.0
Performance fees
Realized	639.5	952.9	267.3
Unrealized	130.8	(99.3)	996.3
Total performance fees	770.3	853.6	1,263.6
Investment income (loss)
Realized	3.3	43.2	4.2
Unrealized	20.5	0.3	40.6
Total investment income (loss)	23.8	43.5	44.8
Interest and other income	9.0	9.2	14.8
Total revenues	1,336.1	1,483.6	1,897.2
Compensation and benefits
Direct base compensation	226.2	253.1	237.6
Indirect base compensation	92.5	90.4	70.9
Equity-based compensation	1.2
Performance fee related
Realized	304.7	487.5	136.0
Unrealized	71.7	(47.1)	524.8
Total compensation and benefits	696.3	783.9	969.3
General, administrative, and other indirect expenses	134.0	133.5	83.5
Depreciation and amortization expense	12.5	14.6	13.7
Interest expense	14.3	37.5	11.4
Total expenses	857.1	969.5	1,077.9
Economic Net Income	479.0	514.1	819.3
Fee Related Earnings	61.3	57.4	171.7
Net performance fees	393.9	413.2	602.8
Realized Net Performance Fees	334.8	465.4	131.3
Investment Income	23.8	43.5	44.8
Distributable Earnings	$ 399.4	$ 566.0	$ 307.2
Segment assets	2,449.4	2,315.2
Global Market Strategies [Member]
Fund level fee revenues
Fund management fees	237.2	173.5	81.9
Portfolio advisory fees, net	2.5	3.0	2.3
Transaction fees, net	3.5		0.1
Total fund level fee revenues	243.2	176.5	84.3
Performance fees
Realized	112.4	204.2	9.8
Unrealized	(21.2)	(92.9)	135.1
Total performance fees	91.2	111.3	144.9
Investment income (loss)
Realized	13.1	20.3	4.8
Unrealized	9.6	12.8	16.9
Total investment income (loss)	22.7	33.1	21.7
Interest and other income	2.3	4.0	2.7
Total revenues	359.4	324.9	253.6
Compensation and benefits
Direct base compensation	86.3	61.7	40.1
Indirect base compensation	21.3	15.1	12.0
Equity-based compensation	0.2
Performance fee related
Realized	46.2	88.4	4.2
Unrealized	(8.4)	(48.2)	70.6
Total compensation and benefits	145.6	117.0	126.9
General, administrative, and other indirect expenses	40.6	33.2	17.6
Depreciation and amortization expense	3.5	2.7	2.5
Interest expense	4.5	10.5	2.6
Total expenses	194.2	163.4	149.6
Economic Net Income	165.2	161.5	104.0
Fee Related Earnings	89.1	57.3	12.2
Net performance fees	53.4	71.1	70.1
Realized Net Performance Fees	66.2	115.8	5.6
Investment Income	22.7	33.1	21.7
Distributable Earnings	$ 168.4	$ 193.4	$ 22.6
Segment assets	1,052.8	1,060.2
Real Assets [Member]
Fund level fee revenues
Fund management fees	141.0	150.7	144.0
Portfolio advisory fees, net	1.7	3.2	2.6
Transaction fees, net	5.0	3.5	8.6
Total fund level fee revenues	147.7	157.4	155.2
Performance fees
Realized	106.6	98.0	(2.9)
Unrealized	(13.2)	52.5	72.7
Total performance fees	93.4	150.5	69.8
Investment income (loss)
Realized	(0.1)	2.1	1.4
Unrealized	(4.9)	2.7	3.7
Total investment income (loss)	(5.0)	4.8	5.1
Interest and other income	1.7	2.0	4.9
Total revenues	237.8	314.7	235.0
Compensation and benefits
Direct base compensation	71.1	75.3	72.4
Indirect base compensation	24.5	28.0	24.2
Equity-based compensation	0.4
Performance fee related
Realized	7.3	8.4	0.5
Unrealized	17.3	(3.9)	(1.6)
Total compensation and benefits	120.6	107.8	95.5
General, administrative, and other indirect expenses	41.9	47.5	40.3
Depreciation and amortization expense	3.9	4.3	4.7
Interest expense	4.4	11.2	3.8
Total expenses	170.8	170.8	144.3
Economic Net Income	67.0	143.9	90.7
Fee Related Earnings	3.2	(6.9)	14.7
Net performance fees	68.8	146.0	70.9
Realized Net Performance Fees	99.3	89.6	(3.4)
Investment Income	(5.0)	4.8	5.1
Distributable Earnings	$ 102.4	$ 84.8	$ 12.7
Segment assets	962.1	566.4
Solutions [Member]
Fund level fee revenues
Fund management fees	68.8	35.0
Total fund level fee revenues	68.8	35.0
Performance fees
Realized	10.6	46.2
Unrealized	30.5	(55.4)
Total performance fees	41.1	(9.2)
Investment income (loss)
Interest and other income	0.7	0.3
Total revenues	110.6	26.1
Compensation and benefits
Direct base compensation	33.8	14.3
Indirect base compensation	6.2
Performance fee related
Realized	8.8	39.5
Unrealized	23.8	(48.8)
Total compensation and benefits	72.6	5.0
General, administrative, and other indirect expenses	10.7	7.3
Depreciation and amortization expense	1.6	0.2
Interest expense	1.3
Total expenses	86.2	12.5
Economic Net Income	24.4	13.6
Fee Related Earnings	15.9	13.5
Net performance fees	8.5	0.1
Realized Net Performance Fees	1.8	6.7
Distributable Earnings	$ 17.7	$ 20.2
Segment assets	342.3	353.1
Reportable Segment Only [Member]
Fund level fee revenues
Fund management fees	943.2	870.5	763.5
Portfolio advisory fees, net	22.0	37.5	19.8
Transaction fees, net	27.5	38.2	30.2
Total fund level fee revenues	992.7	946.2	813.5
Performance fees
Realized	869.1	1,301.3	274.2
Unrealized	126.9	(195.1)	1,204.1
Total performance fees	996.0	1,106.2	1,478.3
Investment income (loss)
Realized	16.3	65.6	10.4
Unrealized	25.2	15.8	61.2
Total investment income (loss)	41.5	81.4	71.6
Interest and other income	13.7	15.5	22.4
Total revenues	2,043.9	2,149.3	2,385.8
Compensation and benefits
Direct base compensation	417.4	404.4	350.1
Indirect base compensation	144.5	133.5	107.1
Equity-based compensation	1.8
Performance fee related
Realized	367.0	623.8	140.7
Unrealized	104.4	(148.0)	593.8
Total compensation and benefits	1,035.1	1,013.7	1,191.7
General, administrative, and other indirect expenses	227.2	221.5	141.4
Depreciation and amortization expense	21.5	21.8	20.9
Interest expense	24.5	59.2	17.8
Total expenses	1,308.3	1,316.2	1,371.8
Economic Net Income	735.6	833.1	1,014.0
Fee Related Earnings	169.5	121.3	198.6
Net performance fees	524.6	630.4	743.8
Realized Net Performance Fees	502.1	677.5	133.5
Investment Income	41.5	81.4	71.6
Distributable Earnings	$ 687.9	$ 864.4	$ 342.5
Segment assets	$ 4,806.6	$ 4,294.9