v2.4.1.9

Commitments and Contingencies (Narrative) (Details)	Dec. 31, 2014 numberofemployees
Number of employees covered under collective bargaining agreements	7,400cmcsa_NumberOfEmployeesCoveredUnderCollectiveBargainingAgreements
Percentage of employees covered under collective bargaining agreements that have expired or are scheduled to expire during 2015	30.00%cmcsa_PercentageOfEmployeesCoveredUnderCollectiveBargainingAgreementsExpiredOrScheduledToExpireDuringNextYear
NBCUniversal Media, LLC [Member]
Number of employees covered under collective bargaining agreements	7,400cmcsa_NumberOfEmployeesCoveredUnderCollectiveBargainingAgreements / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember
Percentage of employees covered under collective bargaining agreements that have expired or are scheduled to expire during 2015	30.00%cmcsa_PercentageOfEmployeesCoveredUnderCollectiveBargainingAgreementsExpiredOrScheduledToExpireDuringNextYear / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember

X

- Definition

Number of NBCUniversal employees on our payroll covered by collective bargaining agreements.

+ References

No definition available.

+ Details

Name:	cmcsa_NumberOfEmployeesCoveredUnderCollectiveBargainingAgreements
Namespace Prefix:	cmcsa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of NBCUniversal full-time equivalent employees that were covered by collective bargaining agreements that have expired or are scheduled to expire during the next year.

+ References

No definition available.

+ Details

Name:	cmcsa_PercentageOfEmployeesCoveredUnderCollectiveBargainingAgreementsExpiredOrScheduledToExpireDuringNextYear
Namespace Prefix:	cmcsa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	cmcsa_LegalEntity1Axis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: