| Cover | May 25, 2021 |
| Schedule of Capitalization, Equity [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 25, 2021 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Class A [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | Class A Common Stock, $0.01 par value |
| Trading Symbol | CMCSA |
| Security Exchange Name | NASDAQ |
| Sec 0. 250 Percent Notes Due 2027 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 0.250% Notes due 2027 |
| Trading Symbol | CMCS27 |
| Security Exchange Name | NASDAQ |
| Sec 1. 500 Percent Notes Due 2029 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 1.500% Notes due 2029 |
| Trading Symbol | CMCS29 |
| Security Exchange Name | NASDAQ |
| Sec 0. 750 Percent Notes Due 2032 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 0.750% Notes due 2032 |
| Trading Symbol | CMCS32 |
| Security Exchange Name | NASDAQ |
| Sec 1. 875 Percent Notes Due 2036 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 1.875% Notes due 2036 |
| Trading Symbol | CMCS36 |
| Security Exchange Name | NASDAQ |
| Sec 1. 250 Percent Notes Due 2040 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 1.250% Notes due 2040 |
| Trading Symbol | CMCS40 |
| Security Exchange Name | NASDAQ |
| Sec 9. 455 Percent Guaranteed Notes Due 2022 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 9.455% Guaranteed Notes due 2022 |
| Trading Symbol | CMCSA/22 |
| Security Exchange Name | NYSE |
| Sec 5. 50 Percent Notes Due 2029 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 5.50% Notes due 2029 |
| Trading Symbol | CCGBP29 |
| Security Exchange Name | NYSE |
| Sec 2. 0 Percent Exchangeable Subordinated Debentures Due 2029 [Member] | |
| Schedule of Capitalization, Equity [Line Items] | |
| Title of 12(b) Security | 2.0% Exchangeable Subordinated Debentures due 2029 |
| Trading Symbol | CCZ |
| Security Exchange Name | NYSE |
