v2.4.1.9

Pension Plans and Postretirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Severance costs | $ 152 us-gaap_SeveranceCosts1 | $ 160 us-gaap_SeveranceCosts1 | $ 155 us-gaap_SeveranceCosts1
Multiemployer Plans Funded Status | At least 80 percent |  |
NBCUniversal Media, LLC [Member] |  |  |
Severance costs | 113 us-gaap_SeveranceCosts1 / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 116 us-gaap_SeveranceCosts1 / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 90 us-gaap_SeveranceCosts1 / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Multiemployer Plans Funded Status | At least 80 percent |  |
Postretirement Benefits [Member] |  |  |
Plan funded status | (837)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (633)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (703)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Postretirement Benefits [Member] | NBCUniversal Media, LLC [Member] |  |  |
Plan funded status | (209)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | (158)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | (177)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Pension Benefits [Member] |  |  |
Multiemployer plan contributions | 58 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 59 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 40 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Plan funded status | (339)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | (278)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | (402)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Contribution to fully fund and settle plan |  | 55 us-gaap_DefinedBenefitPlanSettlementsPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Reclassification adjustment from accumulated other comprehensive income before tax |  | 74 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Pension Benefits [Member] | NBCUniversal Media, LLC [Member] |  |  |
Multiemployer plan contributions | 58 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 59 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 40 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Plan funded status | (339)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | (278)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | (329)us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Deferred Compensation Plans [Member] |  |  |
Cash surrender value of life insurance policies | 628 us-gaap_CashSurrenderValueOfLifeInsurance / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember | 565 us-gaap_CashSurrenderValueOfLifeInsurance / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember |
Retirement Investment Plans [Member] |  |  |
Expenses related to retirement investment plans | 379 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember | 324 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember | 246 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember
Retirement Investment Plans [Member] | NBCUniversal Media, LLC [Member] |  |  |
Expenses related to retirement investment plans | 165 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 152 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 85 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_RetirementInvestmentPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
NBCUniversal Qualified Pension Plan [Member] |  |  |
Plan funded status | 16 us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_NbcuniversalQualifiedPensionPlanMember |  |
NBCUniversal Qualified Pension Plan [Member] | NBCUniversal Media, LLC [Member] |  |  |
Plan funded status | 16 us-gaap_DefinedBenefitPlanFundedStatusOfPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_NbcuniversalQualifiedPensionPlanMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |  |
Benefit obligations in excess of plan assets | 51 us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_NbcuniversalQualifiedPensionPlanMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 43 us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_NbcuniversalQualifiedPensionPlanMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
Postretirement and Other Benefits [Member] |  |  |
Multiemployer plan contributions | 125 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember | 98 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember | 114 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember
Postretirement and Other Benefits [Member] | NBCUniversal Media, LLC [Member] |  |  |
Multiemployer plan contributions | $ 125 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 98 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 114 us-gaap_MultiemployerPlanPeriodContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_PostretirementAndOtherBenefitsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X
- Definition Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity. + 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 210.5-02.17) -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 17 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6812-107765 + Details
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- Definition The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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- Definition If aggregate disclosures are presented, the aggregate fair value of plan assets for plans with benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2417-114920 + Details
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- Definition The amount that relates to an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 15 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(8) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 + Details
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- Definition Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450691-114947 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Indicate whether the multiemployer plan is less than 65 percent funded, between 65 and less than 80 percent funded, or at least 80 percent funded. The acceptable values are: (1) "less than 65 percent", (2) "between 65 and less than 80 percent", (3) "at least 80 percent", and (4) "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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