v2.4.1.9

Long-Term Debt (Debt Maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
2015	$ 4,217us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
2016	3,530us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
2017	2,558us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
2018	4,117us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
2019	2,205us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Thereafter	31,607us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
Weighted average interest rate	4.95%us-gaap_DebtWeightedAverageInterestRate
NBCUniversal Media, LLC [Member]
2015	1,023us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2016	1,008us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2017	2us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2018	2us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2019	2us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Thereafter	$ 8,212us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2015
Weighted average interest rate	4.99%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInOneYearMember
2015 | NBCUniversal Media, LLC [Member]
Weighted average interest rate	3.633%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInOneYearMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2016
Weighted average interest rate	4.158%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInTwoYearsMember
2016 | NBCUniversal Media, LLC [Member]
Weighted average interest rate	2.894%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInTwoYearsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2017
Weighted average interest rate	6.973%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInThreeYearsMember
2017 | NBCUniversal Media, LLC [Member]
Weighted average interest rate	6.296%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInThreeYearsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2018
Weighted average interest rate	4.124%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInFourYearsMember
2018 | NBCUniversal Media, LLC [Member]
Weighted average interest rate	6.307%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInFourYearsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2019
Weighted average interest rate	3.159%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInFiveYearsMember
2019 | NBCUniversal Media, LLC [Member]
Weighted average interest rate	6.329%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_DueInFiveYearsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Thereafter [Member]
Weighted average interest rate	5.425%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_ThereafterMember
Thereafter [Member] | NBCUniversal Media, LLC [Member]
Weighted average interest rate	4.871%us-gaap_DebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cmcsa_ThereafterMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

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X

- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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X

- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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