v3.7.0.1
Commitments and Contingencies - Additional Information (Detail)
$ in Millions
 1 Months Ended 6 Months Ended
Apr. 05, 2017
USD ($)
Mar. 16, 2016
Person
May 31, 2017
ft²
Jun. 30, 2017
USD ($)
Loss Contingencies [Line Items]        
Various capital commitments to fund sponsored investment funds, including funds of private equity funds, real assets funds, opportunistic funds and distressed credit funds       $ 298
Contingent commitments       3
Derivative maximum risk of loss for credit protection       17
Number of former tenants suing BlackRock Parties | Person   3    
Securities lending loan balances indemnified       184,800
Collateral for indemnified securities       $ 198,100
Employee 401(k) Plan [Member]        
Loss Contingencies [Line Items]        
Description of claim sought by former employee under lawsuit complaint       While the complaint does not contain any specific amount in alleged damages, it claims that the purported underperformance and hidden fees cost Plan participants more than $60 million.
Employee 401(k) Plan [Member] | Minimum [Member]        
Loss Contingencies [Line Items]        
Purported underperformance and hidden fees cost $ 60      
Other Liabilities [Member]        
Loss Contingencies [Line Items]        
Contingent consideration at fair value       $ 218
First Reserve Transaction [Member]        
Loss Contingencies [Line Items]        
Contingent consideration at fair value       $ 120
Operating Lease [Member]        
Loss Contingencies [Line Items]        
Area of office space | ft²     847,000  
Operating leases, term of contract     20 years  
Expected lease commencement date       May 31, 2023