v2.4.0.8

Offsetting of Assets and Liabilities - Additional Information (Detail) (Notional Pooling Arrangements, USD $) In Billions, unless otherwise specified | Sep. 30, 2014
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Notional Pooling Arrangements |
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] |
Aggregate cash balance on deposit for cash pooling arrangement | $ 1.2

X
- Definition Amount of cash on deposit related to the entity's cash pooling arrangement. Excludes overdrafts. + References No definition available. + Details
Name: | bx_AggregateCashBalanceOnDepositRelatedToCashPoolingArrangement
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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