Name:	cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesExpectedAmortizationYearOne
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of amortization for right acquired by broadcaster under license agreement for program material, including sports rights advances, expected to be recognized within third operating cycle following most recent annual statement of financial position.

No definition available.

Name:	cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesExpectedAmortizationYearThree
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of amortization for right acquired by broadcaster under license agreement for program material, including sports rights advances, expected to be recognized within second operating cycle following most recent annual statement of financial position.

No definition available.

Name:	cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesExpectedAmortizationYearTwo
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

Name:	us-gaap_EntertainmentLicenseAgreementForProgramMaterialExpectedAmortizationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	us-gaap_FilmCostDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of amortization for completed and not released film predominantly monetized on its own and expected to be recognized within next operating cycle.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483154/926-20-50-4B

Name:	us-gaap_FilmMonetizedOnItsOwnCompletedAndNotReleasedFilmExpectedAmortizationInNextOperatingCycle
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

Name:	us-gaap_FilmMonetizedOnItsOwnReleasedFilmExpectedAmortizationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of amortization for released film predominantly monetized on its own and expected to be recognized within first operating cycle following most recent annual statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483154/926-20-50-4B

Name:	us-gaap_FilmMonetizedOnItsOwnReleasedFilmExpectedAmortizationYearOne
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of amortization for released film predominantly monetized on its own and expected to be recognized within third operating cycle following most recent annual statement of financial position.

Name:	us-gaap_FilmMonetizedOnItsOwnReleasedFilmExpectedAmortizationYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of amortization for released film predominantly monetized on its own and expected to be recognized within second operating cycle following most recent annual statement of financial position.