v2.4.1.9
Document and Entity Information (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Jun. 30, 2014
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2014  
Document Fiscal Year Focus 2014  
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]    
Entity Registrant Name NBCUniversal Media, LLC  
Entity Central Index Key 0000902739  
Entity Filer Category Non-accelerated Filer  
Entity Public Float   $ 0dei_EntityPublicFloat
/ dei_LegalEntityAxis
= cmcsa_NBCUniversalMediaLLCMember
Entity Current Reporting Status Yes  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Class A Common Stock [Member]    
Entity Common Stock, Shares Outstanding 2,131,137,862dei_EntityCommonStockSharesOutstanding
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
 
Entity Public Float   115,221dei_EntityPublicFloat
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Class A Special Common Stock [Member]    
Entity Common Stock, Shares Outstanding 400,484,837dei_EntityCommonStockSharesOutstanding
/ us-gaap_StatementClassOfStockAxis
= cmcsa_ClassaSpecialCommonStockMember
 
Entity Public Float   $ 22,369dei_EntityPublicFloat
/ us-gaap_StatementClassOfStockAxis
= cmcsa_ClassaSpecialCommonStockMember
Class B Common Stock [Member]    
Entity Common Stock, Shares Outstanding 9,444,375dei_EntityCommonStockSharesOutstanding
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember