v2.4.0.8

Investments (Fair Value Method Investments) (Details) (USD $) Share data in Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Fair value equity securities held as collateral | $ 3,959,000,000 | $ 4,143,000,000 |
Obligations under prepaid forward sale agreements | 811,000,000 | 1,248,000,000 |
Derivative component of prepaid forward sale agreements | 2,800,000,000 | 2,302,000,000 |
Total liabilities associated with prepaid forward sale agreements | 3,611,000,000 | 3,550,000,000 |
Prepaid forward sale obligations fair value | 3,600,000,000 | 3,600,000,000 |
Fair value method | 4,345,000,000 | 4,493,000,000 |
Prepaid Forward Obligations Settlement | 1,600,000,000 |  |
Total equity securities used to settle prepaid forward obligations | 1,400,000,000 |  |
Equity securities held as collateral under our prepaid forward sale agreements acquired during the period | 657,000,000 |  |
Proceeds From Sales Of Businesses And Investments | 1,083,000,000 | 3,102,000,000 | 277,000,000
NBCUniversal Media, LLC [Member] |  |  |
Fair value method | 11,000,000 | 21,000,000 |
Clearwire LLC [Member] |  |  |
Proceeds from sale of available-for-sale securities | 443,000,000 |  |
Pre-tax gain realized on Clearwire | 443,000,000 |  |
Fair Value Investment Shares Sold | 89 |  |
Liberty Media Redemption Transaction [Member] |  |  |
Shares Redeemed | 6.3 |  |
Proceeds From Sales Of Businesses And Investments | 417,000,000 |  |
Fair value of the shares delivered in the Liberty Media exchange transaction | $ 937,000,000 |  |

X
- Definition This element represents the fair value as of the balance sheet date of embedded derivative liabilities as a component of prepaid forward sale agreements valued on a recurring basis. + References No definition available. + Details
Name: | cmcsa_DerivativeFairValueOfEmbeddedDerivativeLiabilityComponentOfPrepaidForwardSaleAgreements
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value method equity securities held as collateral related to our obligations under prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_EquitySecuritiesHeldAsCollateral
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash outflow associated with the purchase of all investments during the period that were used to serve as collateral for obligations under prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_EquitySecuritiesPurchasedInPeriod
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair value method equity securities used to settle our obligations under prepaid forward sale agreements in the period. + References No definition available. + Details
Name: | cmcsa_FairValueEquitySecuritiesSettlement
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the amount of Clearwire shares sold to a third party. + References No definition available. + Details
Name: | cmcsa_FairValueInvestmentSharesSold
Namespace Prefix: | cmcsa_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the fair value of the shares delivered in the Liberty Media exchange transaction. + References No definition available. + Details
Name: | cmcsa_FairValueOfSharesDeliveredInTransaction
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The carrying value of the liabilities related to prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_LiabilitiesRelatedToPrepaidForwardSaleAgreements
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The carrying value of obligations related to prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_ObligationsUnderPrepaidForwardSaleAgreements
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The carrying value of obligations related to prepaid forward sale agreements that were settled in the period. + References No definition available. + Details
Name: | cmcsa_PrepaidForwardObligationsSettlement
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The estimated fair value of our prepaid forward sale obligations. + References No definition available. + Details
Name: | cmcsa_PrepaidForwardSaleObligationsFairValue
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash inflow associated with the sale of businesses and investments during the period. + References No definition available. + Details
Name: | cmcsa_ProceedsFromSalesOfBusinessesAndInvestments
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the number of shares held by the Company as a fair value investment which were redeemed by the issuer. + References No definition available. + Details
Name: | cmcsa_SharesRedeemed
Namespace Prefix: | cmcsa_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e689-108580 + Details
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Balance Type: | debit
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- Definition The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26853-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 + Details
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