v2.4.1.9

Borrowings - Additional Information (Detail) (USD $) In Billions, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Debt Instrument [Line Items] |  |
Fair value of the CLO assets | $ 8.2 bx_FairValueOfCLOAssets | $ 8.0 bx_FairValueOfCLOAssets

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