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

Total amounts of capitalized film cost for film predominantly monetized on its own and capitalized cost for rights acquired by broadcaster under license agreement for program material, including sports rights advances.

No definition available.

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

Amounts of capitalized film cost incurred in production and in development of film predominantly monetized on its own

No definition available.

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

- References

No definition available.

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

Amount of capitalized film cost for film predominantly monetized on its own.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483154/926-20-50-2

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

Amount of capitalized film cost for completed and not released film predominantly monetized on its own.

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

Amount of capitalized film cost for released film predominantly monetized on its own.