Accrued Performance Fees - Components of Accrued Giveback Obligations (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Accrued giveback obligations	$ (42.1)	$ (39.6)
Corporate Private Equity [Member]
Segment Reporting Information [Line Items]
Accrued giveback obligations	(27.1)	(10.4)
Global Market Strategies [Member]
Segment Reporting Information [Line Items]
Accrued giveback obligations	(2.1)	(2.1)
Real Assets [Member]
Segment Reporting Information [Line Items]
Accrued giveback obligations	$ (12.9)	$ (27.1)