v2.4.1.9
Equity-Based Compensation - Additional Information (Detail) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Jan. 01, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Partnership grant units     165,943,809us-gaap_UnitsOfPartnershipInterestAmount
Compensation expense in relation to equity-based awards $ 272,335,000us-gaap_ShareBasedCompensation $ 194,645,000us-gaap_ShareBasedCompensation  
Tax benefits in relation to equity-based awards 23,600,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 7,200,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense  
Estimated unrecognized compensation expense related to unvested awards 1,300,000,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized    
Weighted-average period for recognized compensation expense related to unvested awards, years 4 years 9 months 18 days    
Total vested and unvested outstanding units 1,182,828,470us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber    
Phantom Share Units (PSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total outstanding unvested phantom units 1,638us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PhantomShareUnitsPSUsMember
   
Equity-Based Awards With Performance Conditions      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense in relation to equity-based awards $ 2,600,000us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= bx_EquityBasedAwardsWithPerformanceConditionsMember
   
Equity-Based Awards With Performance Conditions | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance period of equity-based awards, in years 3 years    
Equity-Based Awards With Performance Conditions | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance period of equity-based awards, in years 5 years