v2.4.0.6

Fair Value Disclosure Rollforward (Details) (USD $) In Millions, unless otherwise specified | 6 Months Ended
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Jun. 30, 2012
Discount rate used to determine fair value, minimum | 5.60%
Discount rate used to determine fair value, maximum | 13.00%
Contractual Obligations [Member] |
Balance | $ 1,004
Acquisition accounting adjustments | (20)
Fair value adjustments | 41
Payments | (41)
Balance | 984
Contingent Consideration [Member] |
Balance | 583
Acquisition accounting adjustments | 0
Fair value adjustments | 41
Payments | (26)
Balance | $ 598

X
- Definition This element represents the maximum range of the discount rate used to determine the fair value of, but not limited to, 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, but not limited to, 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 the acquisition accounting 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_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisAcquisitionAccountingAdjustments
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
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 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: | instant

X
- Definition This element represents a liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + 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=6925170&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant