v2.4.1.9
Business and Basis of Presentation (Details)
Dec. 31, 2014
numberofcustomers
Mar. 19, 2013
Remaining equity interest acquired   49.00%cmcsa_NoncontrollingInterestAcquired
Total customer relationships 27,000,000cmcsa_Totalcustomerrelationships  
NBCUniversal Media, LLC [Member]    
Remaining equity interest acquired   49.00%cmcsa_NoncontrollingInterestAcquired
/ dei_LegalEntityAxis
= cmcsa_NBCUniversalMediaLLCMember
Video Customers [Member]    
Number of customers 22,400,000cmcsa_NumberOfCustomers
/ us-gaap_StatementBusinessSegmentsAxis
= cmcsa_VideoCustomersMember
 
High-speed Internet Customers [Member]    
Number of customers 22,000,000cmcsa_NumberOfCustomers
/ us-gaap_StatementBusinessSegmentsAxis
= cmcsa_HighSpeedInternetCustomersMember
 
Voice Customers [Member]    
Number of customers 11,200,000cmcsa_NumberOfCustomers
/ us-gaap_StatementBusinessSegmentsAxis
= cmcsa_PhoneCustomersMember