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Investments - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Investment [Line Items]          
Recognized net gains related to equity method investments $ (89.7) $ 97.1 $ 91.9 $ 330.1  
Consolidated Blackstone Funds          
Investment [Line Items]          
Investments $ 454.4   $ 454.4   $ 704.9