Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Jun. 30, 2021
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-32871
Entity Registrant Name	COMCAST CORPORATION
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float		$ 259,633
Documents Incorporated by Reference	Comcast Corporation – Part III – The registrant’s definitive Proxy Statement for its annual meeting of shareholders.
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Fiscal Year Focus	2021
Entity Central Index Key	0001166691
Class A Common Stock
Document 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	4,523,785,950
0.000% Notes due 2026
Document Information [Line Items]
Title of 12(b) Security	0.000% Notes due 2026
Trading Symbol	CMCS26
Security Exchange Name	NASDAQ
0.250% Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	0.250% Notes due 2027
Trading Symbol	CMCS27
Security Exchange Name	NASDAQ
1.500% Notes due 2029
Document Information [Line Items]
Title of 12(b) Security	1.500% Notes due 2029
Trading Symbol	CMCS29
Security Exchange Name	NASDAQ
0.250% Notes due 2029
Document Information [Line Items]
Title of 12(b) Security	0.250% Notes due 2029
Trading Symbol	CMCS29A
Security Exchange Name	NASDAQ
0.750% Notes due 2032
Document Information [Line Items]
Title of 12(b) Security	0.750% Notes due 2032
Trading Symbol	CMCS32
Security Exchange Name	NASDAQ
1.875% Notes due 2036
Document Information [Line Items]
Title of 12(b) Security	1.875% Notes due 2036
Trading Symbol	CMCS36
Security Exchange Name	NASDAQ
1.250% Notes due 2040
Document Information [Line Items]
Title of 12(b) Security	1.250% Notes due 2040
Trading Symbol	CMCS40
Security Exchange Name	NASDAQ
9.455% Guaranteed Notes due 2022
Document Information [Line Items]
Title of 12(b) Security	9.455% Guaranteed Notes due 2022
Trading Symbol	CMCSA/22
Security Exchange Name	NYSE
5.50% Notes due 2029
Document Information [Line Items]
Title of 12(b) Security	5.50% Notes due 2029
Trading Symbol	CCGBP29
Security Exchange Name	NYSE
2.0% Exchangeable Subordinated Debentures due 2029
Document Information [Line Items]
Title of 12(b) Security	2.0% Exchangeable Subordinated Debentures due 2029
Trading Symbol	CCZ
Security Exchange Name	NYSE
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding	9,444,375