v2.4.1.9

Condensed Consolidating Financial Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Comcast Holdings' ZONES due October 2029 [Member]
Debt Instrument, Maturity Date, Description	October 2029
Principal amount of debt securities subject to guarantee	$ 185cmcsa_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	62cmcsa_NonGuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_ComcastHoldingsZonesDueNovember2029Member
NBCUniversal Enterprise Credit Facility [Member]
Debt Instrument, Maturity Date, Description	March 2018
Principal amount of debt securities subject to guarantee	1,350cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = us-gaap_RevolvingCreditFacilityMember
Comcast And Comcast Cable Communications LLC [Member]
Debt Instrument, Maturity Date, Description	June 2017
Principal amount of debt securities subject to guarantee	6,250cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_ComcastAndComcastCableCommunicationsLlcMember
NBCUniversal Enterprise [Member]
Principal amount of debt securities subject to guarantee	$ 4,000cmcsa_GuaranteeObligationsCurrentPrincipalBalance / us-gaap_DerivativeByNatureAxis = cmcsa_NbcuniversalEnterpriseMember

X

- Definition

Principal amount of debt securities subject to guarantee.

+ References

No definition available.

+ Details

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X

- Definition

Principal amount of ZONES not guaranteed by Comcast Corporation, the cable guarantors nor NBCUniversal Media, LLC.

+ References

No definition available.

+ Details

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X

- 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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