Accrued Performance Fees - Components of Accrued Performance Fees (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Line Items]
Accrued performance fees	$ 2,192.5	$ 2,189.1
Corporate Private Equity [Member]
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Line Items]
Accrued performance fees	1,667.3	1,599.2
Global Market Strategies [Member]
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Line Items]
Accrued performance fees	69.5	170.0
Real Assets [Member]
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Line Items]
Accrued performance fees	250.1	270.9
Solutions [Member]
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Line Items]
Accrued performance fees	$ 205.6	$ 149.0