Contribution of a business from member

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Amount of write-off of assets associated with the termination of a merger and/or divestiture transaction recorded in depreciation and amortization expenses.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionSharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

Name:	cmcsa_MemberscontributionthatrepresentedDeferredIncomeTaxAssetsandOtherTaxrelatedItemsrecordedbyParentbutexcludedfromnetassetscontributedAxis=cmcsa_MemberscontributionthatrepresentedDeferredIncomeTaxAssetsandOtherTaxrelatedItemsrecordedbyParentbutexcludedfromnetassetscontributedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	cmcsa_TaxReceivableAgreementAxis=cmcsa_TaxReceivableAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	cmcsa_ConsiderationTransferredByComcastAxis=cmcsa_ConsiderationTransferredByComcastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant Transactions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Aug. 22, 2016	Nov. 13, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
NBCUniversal Media LLC [Member]
Business Acquisition [Line Items]
Contribution from member			$ 3,655	$ 252
DreamWorks Animation [Member]
Business Acquisition [Line Items]
Cash consideration transferred	$ 3,773
Business acquisition share price (in dollars per share)	$ 41
DreamWorks Animation [Member] \| NBCUniversal Media LLC [Member]
Business Acquisition [Line Items]
Cash consideration transferred	$ 3,773
DreamWorks Animation [Member] \| NBCUniversal Media LLC [Member] \| Member's contribution that represented Deferred Income Tax Assets and Other Tax-related Items recorded by Parent but excluded from net assets contributed
Business Acquisition [Line Items]
Contribution from member	353
Universal Studios Japan [Member]
Business Acquisition [Line Items]
Cash consideration transferred		$ 1,499
Ownership percentage		51.00%
Ownership percentage by noncontrolling owners		49.00%
Universal Studios Japan [Member] \| NBCUniversal Media LLC [Member]
Business Acquisition [Line Items]
Cash consideration transferred		$ 1,499
Ownership percentage		51.00%
Ownership percentage by noncontrolling owners		49.00%
Time Warner Cable Merger and Related Divestiture Transactions [Member]
Business Acquisition [Line Items]
Transaction costs and transaction-related costs				198	$ 237
Write-off of assets related to merger agreement termination				$ 20
Tax Receivable Agreement [Member] \| DreamWorks Animation [Member] \| NBCUniversal Media LLC [Member]
Business Acquisition [Line Items]
Contribution from member	146
Cash Consideration Transferred By Comcast [Member] \| DreamWorks Animation [Member] \| NBCUniversal Media LLC [Member]
Business Acquisition [Line Items]
Cash consideration transferred	$ 3,800
Business acquisition share price (in dollars per share)	$ 41