v2.4.0.8
Document and Entity Information (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Jun. 30, 2013
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2013  
Document Fiscal Year Focus 2013  
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 Current Reporting Status Yes  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
NBCUniversal Media, LLC [Member]
    
Amendment Flag false  
Entity Registrant Name NBCUniversal Media, LLC  
Entity Central Index Key 0000902739  
Entity Filer Category Non-accelerated Filer  
Entity Public Float   $ 0
Entity Well-known Seasoned Issuer Yes  
Class A Common Stock [Member]
    
Entity Common Stock, Shares Outstanding 2,138,075,133  
Entity Public Float   88,984
ClassA Special Common Stock [Member]
    
Entity Common Stock, Shares Outstanding 459,030,180  
Entity Public Float   $ 18,733
Class B Common Stock [Member]
    
Entity Common Stock, Shares Outstanding 9,444,375