v3.3.1.900

Investments (Fair Value Method Investments) (Details) - USD ($) shares in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Fair value equity securities held as collateral |  | $ 523 |
Obligations under prepaid forward sale agreements |  | 119 |
Derivative component of prepaid forward sale agreements |  | 356 |
Total liabilities associated with prepaid forward sales agreements | $ 0 | 475 |
Proceeds From Sales Of Businesses And Investments | $ 433 | $ 666 | $ 1,083
Clearwire LLC [Member] |  |  |
Proceeds from sale of available-for-sale securities |  |  | $ 443
Fair Value Investment Shares Sold |  |  | 89.0
Pre-tax gain realized on Clearwire |  |  | $ 443
Liberty Media Redemption Transaction [Member] |  |  |
Shares Redeemed |  |  | 6.3
Fair value of the shares delivered in the Liberty Media exchange transaction |  |  | $ 937
Proceeds From Sales Of Businesses And Investments |  |  | $ 417

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 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 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

X
- 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 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 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e689-108580 Reference 2: 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 3: 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=36458714&loc=d3e637-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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=49167202&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=56944662&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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