v2.4.0.8

Fair Value Disclosure Rollforward (Details) (USD $) In Millions, unless otherwise specified | 6 Months Ended
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Jun. 30, 2014
NBCUniversal Enterprise [Member] |
Fair value of redeemable preferred stock | $ 759
Contractual Obligation [Member] |
Beginning balance | 747
Fair value adjustments | 68
Payments | (27)
Ending balance | 788
Contractual Obligation [Member] | NBCUniversal Media, LLC [Member] |
Beginning balance | 747
Fair value adjustments | 68
Payments | (27)
Ending balance | 788
Discount rate used to determine fair value, minimum | 12.00%
Discount rate used to determine fair value, maximum | 13.00%
Contingent Consideration [Member] |
Beginning balance | 684
Fair value adjustments | 16
Payments | (36)
Ending balance | $ 664
Contractual Obligation And Contingent Consideration Discount Rates [Member] |
Discount rate used to determine fair value, minimum | 5.00%
Discount rate used to determine fair value, maximum | 13.00%

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 Fair value of our redeemable subsidiary preferred stock. + References No definition available. + Details
Name: | cmcsa_FairValueAmountOfRedeemablePreferredStock
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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 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 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