v3.3.0.814

Information for Financial Instruments on Which Fair Value Option was Elected (Parenthetical) (Detail) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2015 | Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Loans and bonds contractual payment past due, number days | 1 day | 1 day

X
- Definition Loans And Bonds Contractual Payment Past Due Number Days + References No definition available. + Details
Name: | bx_LoansAndBondsContractualPaymentPastDueNumberDays
Namespace Prefix: | bx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration