v2.4.0.8

Borrowings - Additional Information (Detail) (USD $) In Billions, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Debt Instrument [Line Items] |  |
Fair value of the CLO assets | $ 9.9 | $ 12.5

X
- Definition Fair Value of the CLO Assets + References No definition available. + Details
Name: | bx_FairValueOfCLOAssets
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration