Accrued Performance Fees - Performance Fees (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Statistics [Line Items]
Performance Fees	$ 1,041.1	$ 1,121.6	$ 1,482.0
Corporate Private Equity [Member]
Operating Statistics [Line Items]
Performance Fees	786.1	845.8	1,259.0
Global Market Strategies [Member]
Operating Statistics [Line Items]
Performance Fees	99.6	145.9	144.6
Real Assets [Member]
Operating Statistics [Line Items]
Performance Fees	90.7	150.4	78.4
Solutions [Member]
Operating Statistics [Line Items]
Performance Fees	$ 64.7	$ (20.5)