v2.4.0.8

Fair Value Disclosure Rollforward (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012
Discount rate used to determine fair value, minimum | 5.00% |
Discount rate used to determine fair value, maximum | 13.00% |
Nonrecurring fair value adjustments | $ 167 | $ 161
NBCUniversal Media, LLC [Member] |  |
Discount rate used to determine fair value, minimum | 12.00% |
Discount rate used to determine fair value, maximum | 13.00% |
Nonrecurring fair value adjustments | 167 | 161
Contractual Obligations [Member] |  |
Beginning balance | 1,055 |
Fair value adjustments | 158 |
Payments | (83) |
Liberty Media transaction | (383) |
Ending balance | 747 |
Contractual Obligations [Member] | NBCUniversal Media, LLC [Member] |  |
Beginning balance | 1,055 |
Fair value adjustments | 158 |
Payments | (83) |
Liberty Media transaction | (383) |
Ending balance | 747 |
Contingent Consideration [Member] |  |
Beginning balance | 587 |
Fair value adjustments | 106 |
Payments | (214) |
Redemption transaction | 205 |
Ending balance | $ 684 |

X
- Definition This element represents the maximum range of the discount rate used to determine the fair value of contractual obligations and contingent considerations. + References No definition available. + Details
Name: | cmcsa_DiscountRateUsedToDetermineFairValueMaximum
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the minimum range of the discount rate used to determine the fair value of contractual obligations and contingent considerations. + References No definition available. + Details
Name: | cmcsa_DiscountRateUsedToDetermineFairValueMinimum
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents other fair value adjustments recorded during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
Name: | cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisFairValueAdjustment
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents adjustments to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy in relation to the Libety Media transaction. + References No definition available. + Details
Name: | cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLibertyMediaTransaction
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This element represents the payments made during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
Name: | cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisPayments
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents adjustments to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy in relation to the redemption transaction. + References No definition available. + Details
Name: | cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisRedemptionTransaction
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + 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 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228 + Details
Name: | us-gaap_AssetImpairmentCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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=25499696&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant