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

Fair value of our redeemable subsidiary preferred stock.

No definition available.

Name:	cmcsa_FairValueAmountOfRedeemablePreferredStock
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 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

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