v2.4.1.9

Long-Term Debt (Debt Maturities) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014
--- | ---
2015 | $ 4,217 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
2016 | 3,530 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
2017 | 2,558 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
2018 | 4,117 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
2019 | 2,205 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Thereafter | 31,607 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
Weighted average interest rate | 4.95%us-gaap_DebtWeightedAverageInterestRate
NBCUniversal Media, LLC [Member] |
2015 | 1,023 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2016 | 1,008 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2017 | 2 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2018 | 2 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
2019 | 2 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Thereafter | $ 8,212 us-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. + Details
Name: | us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_DueInFiveYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_DueInFourYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_DueInOneYearMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_DueInThreeYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_DueInTwoYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_ThereafterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |