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

- Definition

Projected cash to be paid for all of the outstanding stock of an entity in a future acquisition.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	cmcsa_SignificantTransactionsLineItems
Namespace Prefix:	cmcsa_
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

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.

+ References

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

+ Details

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

- Definition

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

+ References

+ Details

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
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

- Definition

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

+ References

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

+ Details

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

- Details

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

- Details

Name:	dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
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:

Significant Transactions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	6 Months Ended
	Nov. 13, 2015	Jun. 30, 2016	Jun. 30, 2016
DreamWorks Animation [Member]
Significant Transactions [Line Items]
Business Acquisition, Share Price		$ 41	$ 41
Business Acquistion, Purchase Price for Future Acquisition			$ 3,800
DreamWorks Animation [Member] \| NBCUniversal Media LLC [Member]
Significant Transactions [Line Items]
Business Acquisition, Share Price		$ 41	$ 41
Business Acquistion, Purchase Price for Future Acquisition			$ 3,800
Universal Studios Japan [Member]
Significant Transactions [Line Items]
Ownership Percentage	51.00%
Cash Consideration Transferred	$ 1,500
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	49.00%
Revenue Of Acquiree Since Acquisition Date		$ 283	576
Net income (loss) attributable to acquired company		10	28
Universal Studios Japan [Member] \| NBCUniversal Media LLC [Member]
Significant Transactions [Line Items]
Ownership Percentage	51.00%
Cash Consideration Transferred	$ 1,500
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	49.00%
Revenue Of Acquiree Since Acquisition Date		283	576
Net income (loss) attributable to acquired company		$ 10	$ 28