v3.8.0.1
Document and Entity Information
9 Months Ended
Sep. 30, 2017
shares
Document And Entity Information [Line Items]  
Entity Registrant Name COMCAST CORP
Entity Central Index Key 0001166691
Trading Symbol cmcsa
Current Fiscal Year End Date --12-31
Entity Filer Category Large Accelerated Filer
Document Type 10-Q
Document Period End Date Sep. 30, 2017
Document Fiscal Year Focus 2017
Document Fiscal Period Focus Q3
Amendment Flag false
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
Class A Common Stock [Member]  
Document And Entity Information [Line Items]  
Entity Common Stock, Shares Outstanding 4,664,327,455
Class B Common Stock [Member]  
Document And Entity Information [Line Items]  
Entity Common Stock, Shares Outstanding 9,444,375