v3.8.0.1
Commitments and Contingencies - Additional Information (Detail)
$ in Millions
 3 Months Ended
Mar. 16, 2016
Person
Mar. 31, 2018
USD ($)
ft²
Dec. 31, 2017
USD ($)
Commitment And 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   $ 304  
Derivative maximum risk of loss for credit protection   17 $ 17
Number of former tenants suing BlackRock Parties | Person 3    
Securities lending loan balances indemnified   219,000  
Collateral for indemnified securities   $ 232,000  
Employee 401(k) Plan [Member]      
Commitment And 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]      
Commitment And Contingencies [Line Items]      
Purported underperformance and hidden fees cost   $ 60  
Other Liabilities [Member]      
Commitment And Contingencies [Line Items]      
Contingent consideration at fair value   $ 242  
Operating Lease [Member]      
Commitment And Contingencies [Line Items]      
Area of office space | ft²   847,000  
Operating leases, term of contract   20 years  
Expected lease commencement date   May 31, 2023  
Annual base rental payments first five years   $ 51  
Annual base rental payments five to ten years   58  
Annual base rental payments ten to fifteen years   66  
Annual base rental payments fifteen to twenty years   74  
Total operating lease minimum commitments   $ 1,200