Document and Entity Information	6 Months Ended
	Jun. 30, 2019 shares
Document And Entity Information [Line Items]
Document Type	10-Q
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Current Fiscal Year End Date	--12-31
Entity File Number	001-32871
Entity Registrant Name	COMCAST CORPORATION
Entity Central Index Key	0001166691
Entity Tax Identification Number	27-0000798
Entity Incorporation, State or Country Code	PA
Entity Address, Address Line One	One Comcast Center
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19103-2838
City Area Code	215
Local Phone Number	286-1700
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
NBCUniversal Media LLC [Member]
Document And Entity Information [Line Items]
Entity File Number	001-36438
Entity Registrant Name	NBCUNIVERSAL MEDIA, LLC
Entity Central Index Key	0000902739
Entity Tax Identification Number	14-1682529
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	30 Rockefeller Plaza
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10112-0015
City Area Code	212
Local Phone Number	664-4444
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
2.0% Exchangeable Subordinated Debentures Due 2029 [Member]
Document And Entity Information [Line Items]
Title of 12(b) Security	2.0% Exchangeable Subordinated Debentures due 2029
Trading Symbol	CCZ
Security Exchange Name	NYSE
5.50% Notes Due 2029 [Member]
Document And Entity Information [Line Items]
Title of 12(b) Security	5.50% Notes due 2029
Trading Symbol	CCGBP29
Security Exchange Name	NYSE
9.455% Guaranteed Notes Due 2022 [Member]
Document And Entity Information [Line Items]
Title of 12(b) Security	9.455% Guaranteed Notes due 2022
Trading Symbol	CMCSA/22
Security Exchange Name	NYSE
Class A Common Stock [Member]
Document And Entity Information [Line Items]
Title of 12(b) Security	Class A Common Stock, $0.01 par value
Trading Symbol	CMCSA
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding	4,535,540,993
Class B Common Stock [Member]
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding	9,444,375