Name:	cmcsa_DiscountRateUsedToDetermineFairValueMaximum
Namespace Prefix:	cmcsa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

This element represents the minimum range of the discount rate used to determine the fair value of contractual obligations and contingent considerations.

No definition available.

Name:	cmcsa_DiscountRateUsedToDetermineFairValueMinimum
Namespace Prefix:	cmcsa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisFairValueAdjustment
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLibertyMediaTransaction
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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.

No definition available.

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisPayments
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisRedemptionTransaction
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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.

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

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

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