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

The total consideration associated with the purchase of GE's 49% noncontrolling common equity interest in NBCUniversal.

No definition available.

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

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

Represents the percentage of voting interest acquired at the acquisition date from a noncontrolling interest.

No definition available.

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

Represents the ownership percentage in NBCUniversal Holdings.

No definition available.

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

The parent entity's interest in net assets of the subsidiary, expressed as a percentage

No definition available.

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

The total purchase price for acquisitions of real estate properties.

No definition available.

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

Portion of consideration transferred related to the Redemption Transaction and purchase of certain properties funded by NBCUniversal.

No definition available.

Name:	cmcsa_PortionOfConsiderationTransferredFundedByNbcuniversal
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The description of the percentage rate used to calculate dividend payments on preferred stock at the future reset date.

No definition available.

Name:	cmcsa_PreferredStockDividendResetRatePercentage
Namespace Prefix:	cmcsa_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The percentage of preferred units that NBCUniversal Enterprise owns for which NBCUniversal Enterprise has the right to cause NBCUniversal Holdings to redeem at a future date.

No definition available.

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

- References

No definition available.

Name:	cmcsa_SignificantTransactionsLineItems
Namespace Prefix:	cmcsa_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Transaction costs and transaction related costs recorded in the statement of income.

No definition available.

Name:	cmcsa_Transactioncostsandtransactionrelatedcosts
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of write-off of assets associated with the termination of the Time Warner Cable merger and the divestiture transactions recorded in depreciation and amortization expenses.

No definition available.

Name:	cmcsa_WriteOffofassetsrelatedtomergeragreementtermination
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

Name:	us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

Name:	us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The percentage rate used to calculate dividend payments on preferred stock.

No definition available.

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

No definition available.

Name:	us-gaap_PreferredStockLiquidationPreferenceValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_ComcastCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=us-gaap_CashMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_NbcuniversalcashonhandmemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=us-gaap_PreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_NBCUniversalHoldingsPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_ThirtyRockefellerPlazaAndEnglewoodCliffsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_NbcuniversalEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_TransactionRelatedExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_UniversalStudiosJapanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=cmcsa_NbcuniversalEnterpriseCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: