v2.4.0.8

Offsetting of Assets and Liabilities - Additional Information (Detail) (Notional Pooling Arrangements, USD $) In Billions, unless otherwise specified	Sep. 30, 2014
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