Cover Page
| Cover Page | Feb. 05, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 5, 2020 |
| Entity Registrant Name | COMCAST CORP |
| Entity Central Index Key | 0001166691 |
| Entity Incorporation, State or Country Code | PA |
| Entity File Number | 001-32871 |
| Entity Tax Identification Number | 27-0000798 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| NBCUniversal Media LLC [Member] | |
| Document Information [Line Items] | |
| Entity Registrant Name | NBCUniversal Media, LLC |
| Entity Central Index Key | 0000902739 |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36438 |
| Entity Tax Identification Number | 14-1682529 |
| 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 Emerging Growth Company | false |
| Class A Common Stock, $0.01 par value [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class A Common Stock, $0.01 par value |
| Trading Symbol | CMCSA |
| Security Exchange Name | NASDAQ |
| 2.0% Exchangeable Subordinated Debentures due 2029 [Member] | |
| Document 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 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 Information [Line Items] | |
| Title of 12(b) Security | 9.455% Guaranteed Notes due 2022 |
| Trading Symbol | CMCSA/22 |
| Security Exchange Name | NYSE |