v2.4.1.9
Long-Term Debt (Details)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2014
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2013
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2014
Revolving bank credit facility [Member]
Dec. 31, 2014
Commercial Paper Program
Dec. 31, 2014
Senior notes with maturities of 5 years or less [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities of 5 years or less [Member]
USD ($)
Dec. 31, 2014
Senior notes with maturities of 5 years or less [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities of 5 years or less [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2014
Senior notes with maturities between 5 and 10 years [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities between 5 and 10 years [Member]
USD ($)
Dec. 31, 2014
Senior notes with maturities between 5 and 10 years [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities between 5 and 10 years [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2014
Senior notes with maturities greater than 10 years [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities greater than 10 years [Member]
USD ($)
Dec. 31, 2014
Senior notes with maturities greater than 10 years [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2013
Senior notes with maturities greater than 10 years [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2014
Other Including Capital Lease Obligations [Member]
USD ($)
Dec. 31, 2013
Other Including Capital Lease Obligations [Member]
USD ($)
Dec. 31, 2014
Other Including Capital Lease Obligations [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2013
Other Including Capital Lease Obligations [Member]
NBCUniversal Media, LLC [Member]
USD ($)
Dec. 31, 2014
Notes 5.50% Due 2029 [Member]
USD ($)
Dec. 31, 2014
Notes 5.50% Due 2029 [Member]
GBP (£)
Dec. 31, 2013
Notes 5.50% Due 2029 [Member]
USD ($)
Dec. 31, 2013
Notes 5.50% Due 2029 [Member]
GBP (£)
Commercial paper $ 845,000,000us-gaap_CommercialPaper $ 1,350,000,000us-gaap_CommercialPaper                                                
Revolving credit facilities 0us-gaap_LineOfCreditFacilityAmountOutstanding 1,250,000,000us-gaap_LineOfCreditFacilityAmountOutstanding                                                
Senior notes             15,334,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
15,080,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
2,005,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
2,917,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
10,527,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
11,533,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
4,996,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
4,996,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
20,937,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
18,010,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
3,204,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
3,205,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
        974,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_Notes550Due2029Member
625,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_Notes550Due2029Member
1,000,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_Notes550Due2029Member
625,000,000us-gaap_SeniorNotes
/ us-gaap_DebtInstrumentAxis
= cmcsa_Notes550Due2029Member
Other, including capital lease obligations                                     591,000,000us-gaap_OtherBorrowings
/ us-gaap_DebtInstrumentAxis
= cmcsa_OtherIncludingCapitalLeaseObligationsMember
624,000,000us-gaap_OtherBorrowings
/ us-gaap_DebtInstrumentAxis
= cmcsa_OtherIncludingCapitalLeaseObligationsMember
44,000,000us-gaap_OtherBorrowings
/ us-gaap_DebtInstrumentAxis
= cmcsa_OtherIncludingCapitalLeaseObligationsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
47,000,000us-gaap_OtherBorrowings
/ us-gaap_DebtInstrumentAxis
= cmcsa_OtherIncludingCapitalLeaseObligationsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
       
Total debt 48,234,000,000us-gaap_DebtAndCapitalLeaseObligations 47,847,000,000us-gaap_DebtAndCapitalLeaseObligations 10,249,000,000us-gaap_DebtAndCapitalLeaseObligations
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
11,165,000,000us-gaap_DebtAndCapitalLeaseObligations
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
                                           
Less: current portion 4,217,000,000us-gaap_DebtCurrent 3,280,000,000us-gaap_DebtCurrent 1,023,000,000us-gaap_DebtCurrent
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
906,000,000us-gaap_DebtCurrent
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
                                           
Long-term debt, less current portion $ 44,017,000,000us-gaap_LongTermDebtAndCapitalLeaseObligations $ 44,567,000,000us-gaap_LongTermDebtAndCapitalLeaseObligations $ 9,226,000,000us-gaap_LongTermDebtAndCapitalLeaseObligations
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
$ 10,259,000,000us-gaap_LongTermDebtAndCapitalLeaseObligations
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
                                           
Weighted average interest rate 4.95%us-gaap_DebtWeightedAverageInterestRate   4.46%us-gaap_DebtWeightedAverageInterestRate
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
  0.00%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_RevolvingBankCreditFacilityMember
0.373%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= us-gaap_CommercialPaperMember
4.642%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
  3.254%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesOf5YearsOrLessMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
  4.822%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
  4.389%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesBetween5And10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember
  5.737%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
  5.614%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= cmcsa_SeniorNotesWithMaturitiesGreaterThan10YearsMember
/ cmcsa_LegalEntity1Axis
= cmcsa_NBCUniversalMediaLLCMember