v2.4.0.8

Long-Term Debt (Narrative) (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Long-term Debt, Fair Value | $ 51,800,000,000 | $ 47,700,000,000 |
Revolving credit facilities | 1,250,000,000 |  |
Amounts available under revolving credit facilities | 4,700,000,000 |  |
Repurchases and repayments of debt | 2,444,000,000 | 2,881,000,000 | 3,216,000,000
Unused irrevocable standby letters of credit | 515,000,000 |  |
Commercial paper prior borrowing capacity [Member] |  |  |
Credit facility borrowing capacity | 2,250,000,000 |  |
NBCUniversal Media, LLC [Member] |  |  |
Long-term Debt, Fair Value | 11,700,000,000 | 12,600,000,000 |
NBCUniversal Enterprise Senior Unsecured Debt Securities |  |  |
Consideration transferred related to the Redemption Transaction and purchase of certain properties | 4,000,000,000 |  |
Comcast Commercial Paper Program |  |  |
Consideration transferred related to the Redemption Transaction and purchase of certain properties | 750,000,000 |  |
NBCUniversal Enterprise Credit Facility |  |  |
Consideration transferred related to the Redemption Transaction and purchase of certain properties | 1,250,000,000 |  |
Amounts available under revolving credit facilities | 100,000,000 |  |
Comcast And Comcast Cable Communications LLC [Member] |  |  |
Debt Instrument, Maturity Date, Description | June 2017 |  |
Credit facility borrowing capacity | 6,250,000,000 |  |
Comcast And Comcast Cable Communications LLC [Member] | NBCUniversal Media, LLC [Member] |  |  |
Debt Instrument, Maturity Date, Description | June 2017 |  |
Credit facility borrowing capacity | 6,250,000,000 |  |
Guarantee Obligations Current Principal Balance | 31,000,000,000 |  |
NBCUniversal Enterprise [Member] | NBCUniversal Media, LLC [Member] |  |  |
Principal amount | 4,000,000,000 |  |
Preferred stock liquidition preference value | 725,000,000 |  |
Senior 1.662% Notes Due 2018 [Member] | NBCUniversal Enterprise [Member] |  |  |
Principal amount | 1,100,000,000 |  |
Interest rate | 1.662% |  |
Debt Instrument, Maturity Date, Description | 2018 |  |
Senior 1.974% Notes Due 2019 [Member] | NBCUniversal Enterprise [Member] |  |  |
Principal amount | 1,500,000,000 |  |
Interest rate | 1.974% |  |
Debt Instrument, Maturity Date, Description | 2019 |  |
Floating Rate Senior Notes Due 2018 [Member] | NBCUniversal Enterprise [Member] |  |  |
Principal amount | 700,000,000 |  |
Debt Instrument, Maturity Date, Description | 2018 |  |
Spread above LIBOR offered rate | 0.685% |  |
Floating Rate Senior Notes Due 2016 [Member] | NBCUniversal Enterprise [Member] |  |  |
Principal amount | 700,000,000 |  |
Debt Instrument, Maturity Date, Description | 2016 |  |
Spread above LIBOR offered rate | 0.537% |  |
Other Long-Term Debt [Member] |  |  |
Repurchases and repayments of debt | 109,000,000 |  |
Notes 5.50% Due 2029 [Member] |  |  |
Interest rate | 5.50% | 5.50% |
Debt Instrument, Maturity Date, Description | 2029 | 2029 |
Senior 2.850% Notes Due 2023 [Member] |  |  |
Principal amount | 750,000,000 |  |
Interest rate | 2.85% |  |
Debt Instrument, Maturity Date, Description | 2023 |  |
Senior 4.250% Notes Due 2033 [Member] |  |  |
Principal amount | 1,700,000,000 |  |
Interest rate | 4.25% |  |
Debt Instrument, Maturity Date, Description | 2033 |  |
Senior 4.500% Notes Due 2043 [Member] |  |  |
Principal amount | 500,000,000 |  |
Interest rate | 4.50% |  |
Debt Instrument, Maturity Date, Description | 2043 |  |
Current Year Borrowings [Member] |  |  |
Principal amount | 2,950,000,000 |  |
Prior NBCUniversal Credit Facility [Member] |  |  |
Credit facility borrowing capacity | 1,500,000,000 |  |
NBCUniversal Enterprise Credit Facility [Member] |  |  |
Debt Instrument, Maturity Date, Description | March 2018 |  |
Credit facility borrowing capacity | 1,350,000,000 |  |
NBCUniversal Enterprise Credit Facility [Member] | NBCUniversal Media, LLC [Member] |  |  |
Credit facility borrowing capacity | 1,350,000,000 |  |
Senior 8.375% Notes Due 2013 [Member] |  |  |
Interest rate | 8.375% |  |
Debt Instrument, Maturity Date, Description | 2013 |  |
Repurchases and repayments of debt | 1,714,000,000 |  |
Senior 7.125% Notes Due 2013 [Member] |  |  |
Interest rate | 7.125% |  |
Debt Instrument, Maturity Date, Description | 2013 |  |
Repurchases and repayments of debt | 383,000,000 |  |
Senior 7.875% Notes Due 2013 [Member] |  |  |
Interest rate | 7.875% |  |
Debt Instrument, Maturity Date, Description | 2013 |  |
Repurchases and repayments of debt | $ 238,000,000 |  |

X
- Definition The consideration associated with the purchase of GE's 49% noncontrolling common equity interest in NBCUniversal related to the Redemption Transaction and the acquisition of certain properties at 30 Rockefeller Plaza and Engelwood Cliffs. + References No definition available. + Details
Name: | cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Principal amount of debt securities subject to guarantee. + References No definition available. + Details
Name: | cmcsa_GuaranteeObligationsCurrentPrincipalBalance
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + 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)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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 + Details
Name: | us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount borrowed under the credit facility as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + 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 -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Value of the difference between preference in liquidation and the par or stated values of the preferred shares. + References No definition available. + Details
Name: | us-gaap_PreferredStockLiquidationPreferenceValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash outflow for the payment of other borrowing not otherwise defined in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 + Details
Name: | us-gaap_RepaymentsOfOtherDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration