Document and Entity Information	6 Months Ended
	Jun. 30, 2013
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2
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
Class A Common Stock [Member]
Entity Common Stock, Shares Outstanding	2,133,605,012
ClassA Special Common Stock [Member]
Entity Common Stock, Shares Outstanding	481,862,157
Class B Common Stock [Member]
Entity Common Stock, Shares Outstanding	9,444,375