v2.4.1.9

Fair Value Disclosure Rollforward (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
NBCUniversal Enterprise [Member] |
Fair value of redeemable preferred stock | $ 764 cmcsa_FairValueAmountOfRedeemablePreferredShares / dei_LegalEntityAxis = cmcsa_NbcuniversalEnterpriseMember
Contractual Obligations [Member] |
Beginning balance | 883 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember
Fair value adjustments | 40 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember
Payments | (19)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember
Ending balance | 904 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember
Contractual Obligations [Member] | NBCUniversal Media, LLC [Member] |
Beginning balance | 883 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Fair value adjustments | 40 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Payments | (19)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Ending balance | 904 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_ObligationsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Contingent Consideration [Member] |
Beginning balance | 644 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = cmcsa_ContingentConsiderationMember
Fair value adjustments | 7 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease / us-gaap_FairValueByLiabilityClassAxis = cmcsa_ContingentConsiderationMember
Payments | (19)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements / us-gaap_FairValueByLiabilityClassAxis = cmcsa_ContingentConsiderationMember
Ending balance | $ 632 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = cmcsa_ContingentConsiderationMember
Maximum [Member] |
Discount Rate Used To Determine Fair Value | 13.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_MaximumMember
Maximum [Member] | NBCUniversal Media, LLC [Member] |
Discount Rate Used To Determine Fair Value | 13.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_MaximumMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Minimum [Member] |
Discount Rate Used To Determine Fair Value | 5.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_MinimumMember
Minimum [Member] | NBCUniversal Media, LLC [Member] |
Discount Rate Used To Determine Fair Value | 12.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_MinimumMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

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- Definition Fair value of our redeemable subsidiary preferred shares and/or stock + References No definition available. + Details
Name: | cmcsa_FairValueAmountOfRedeemablePreferredShares
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of increase (decrease) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=cmcsa_ContingentConsiderationMember
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Data Type: | na
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- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=us-gaap_MaximumMember
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- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=us-gaap_MinimumMember
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- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=us-gaap_ObligationsMember
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Data Type: | na
Balance Type: |
Period Type: |