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Significant business acquisitions - Narrative (Detail)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Feb. 29, 2016
USD ($)
Jan. 29, 2016
USD ($)
$ / shares
Mar. 31, 2015
USD ($)
Business
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Business Acquisition [Line Items]            
Fair value of shares exchanged         $ 4,239  
Precision Castparts Corp. [Member]            
Business Acquisition [Line Items]            
Business acquisition, cash price per share | $ / shares   $ 235        
Aggregate consideration paid for business acquisition   $ 32,700        
Duracell Company [Member] | Procter & Gamble Company [Member]            
Business Acquisition [Line Items]            
Fair value of shares exchanged $ 4,239          
Series of Individually Immaterial Business Acquisitions [Member]            
Business Acquisition [Line Items]            
Aggregate consideration paid for acquisitions       $ 2,700 $ 1,400 $ 1,100
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member]            
Business Acquisition [Line Items]            
Aggregate consideration paid for acquisitions     $ 4,100      
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member] | Insurance [Member]            
Business Acquisition [Line Items]            
Number of businesses | Business     2      
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member] | Auto Auctions [Member]            
Business Acquisition [Line Items]            
Number of businesses | Business     2      
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member] | Distributor of Automotive Fluid Maintenance Products [Member]            
Business Acquisition [Line Items]            
Number of businesses | Business     1      
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member] | Minimum [Member] | Auto Dealerships [Member]            
Business Acquisition [Line Items]            
Number of businesses | Business     80