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Document and Entity Information
 3 Months Ended
Mar. 31, 2019
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
Entity Emerging Growth Company false
Entity Small Business false
Document Type 10-Q
Document Period End Date Mar. 31, 2019
Document Fiscal Year Focus 2019
Document Fiscal Period Focus Q1
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
Entity Emerging Growth Company false
Entity Small Business false
Class A Common Stock [Member]  
Document And Entity Information [Line Items]  
Entity Common Stock, Shares Outstanding 4,529,070,833
Class B Common Stock [Member]  
Document And Entity Information [Line Items]  
Entity Common Stock, Shares Outstanding 9,444,375