Segment Reporting - Reconciliation of Income Before Provision for Income Taxes to Distributed Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Statistics [Line Items]
Income (loss) before provision for income taxes	$ 145.5	$ 602.5	$ 186.1	$ 1,505.8	$ 712.4	$ (619.2)	$ 317.3	$ 772.3	$ 2,439.9	$ 1,182.8	$ 1,479.7
Adjustments:
Partner compensation									(265.4)	(671.5)	(768.2)
Equity-based compensation issued in conjuction with the initial public offering									200.1
Acquisition related charges and amortization of intangibles									128.3	91.5	11.0
Gain on business acquisition										(7.9)
Equity issued for affiliate debt financing											214.0
Other non-operating expenses									7.1	32.0
Losses associated with early extinguishment of debt											2.5
Net income attributable to non-controlling interests in consolidated entities									(1,756.7)	202.6	66.2
Provision for income taxes attributable to non-controlling interests in consolidated entities									(19.5)
Severance and lease terminations									5.9	4.5	8.5
Other adjustments									(4.1)	(0.9)	0.3
Economic Net Income									735.6	833.1	1,014.0
Net performance fees									524.6	630.4	743.8
Investment income									41.5	81.4	71.6
Fee Related Earnings									169.5	121.3	198.6
Realized performance fees, net of related compensation									502.1	677.5	133.5
Investment income-realized									$ 16.3	$ 65.6	$ 10.4
Distributable Earnings									$ 687.9	$ 864.4	$ 342.5