v2.4.1.9

Condensed Consolidating Financial Information (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
Comcast Holdings' ZONES due October 2029 [Member]
Debt Instrument, Maturity Date, Description	October 2029
Principal amount of debt securities subject to guarantee	$ 185,000,000cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_ComcastHoldingsZonesDueOctober2029Member
Comcast Holdings' ZONES due November 2029 [Member]
Debt Instrument, Maturity Date, Description	November 2029
Principal amount of debt securities not subject to guarantee	62,000,000cmcsa_NonGuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_ComcastHoldingsZonesDueNovember2029Member
Guarantor Subsidiaries [Member]
Principal amount of debt securities subject to guarantee	32,600,000,000cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = us-gaap_GuarantorSubsidiariesMember
Maturing In Next Five Years [Member]
Principal amount of debt securities subject to guarantee	9,300,000,000cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_MaturingInNextFiveYearsMember
NBCUniversal Enterprise Credit Facility [Member]
Debt Instrument, Maturity Date, Description	March 2018
Credit facility borrowing capacity	1,350,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DerivativeByNatureAxis = us-gaap_RevolvingCreditFacilityMember
Comcast And Comcast Cable Communications LLC [Member]
Debt Instrument, Maturity Date, Description	June 2017
Credit facility borrowing capacity	6,250,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DerivativeByNatureAxis = cmcsa_ComcastAndComcastCableCommunicationsLlcMember
NBCUniversal Enterprise [Member]
Principal amount of debt securities subject to guarantee	$ 4,000,000,000cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_NbcuniversalEnterpriseMember

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+ References

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- Definition

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+ References

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- Definition

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 2: http://www.xbrl.org/2003/role/presentationRef

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