Related Party Transactions - Due from Affiliates and Other Receivables (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Related Party Transaction [Line Items]
Total	$ 190.7	$ 287.0
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Unbilled receivable for giveback obligations from current and former employees	32.8	56.5
Notes receivable and accrued interest from affiliates	10.0	56.8
Other receivables from unconsolidated funds and affiliates, net	$ 147.9	$ 173.7