v3.6.0.2
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Jun. 30, 2016
Document And Entity Information [Line Items]    
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus FY  
Trading Symbol cmcsa  
Entity Registrant Name COMCAST CORP  
Entity Central Index Key 0001166691  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Public Float   $ 155,940
Entity Current Reporting Status Yes  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
NBCUniversal Media LLC [Member]    
Document And Entity Information [Line Items]    
Entity Registrant Name NBCUniversal Media, LLC  
Entity Central Index Key 0000902739  
Entity Filer Category Non-accelerated Filer  
Entity Public Float   $ 0
Entity Current Reporting Status Yes  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Class A Common Stock [Member]    
Document And Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding 2,366,357,318  
Class B Common Stock [Member]    
Document And Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding 9,444,375