Capital contribution to a VIE recorded in the current period to be paid in a future period.

No definition available.

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Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow associated with a capital contribution to a VIE accounted for as an equity method investment

+ References

No definition available.

+ Details

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

- Definition

This element represents disclosure of the amount of gain which has been deferred as the result of a dilution in our ownership percentage in an equity method investment which deferred gain has been reflected in the accompanying statement of financial position.

+ References

No definition available.

+ Details

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

- Definition

Equity Method Investment, Funding Commitment

+ References

No definition available.

+ Details

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

- Definition

Equity Method Investment, Funding Commitment by Management Company Investors

+ References

No definition available.

+ Details

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

- Definition

Equity Method Investment, Management Fee Funding Commitment

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of any losses in an equity method investment that the Company is obligated to absorb.

+ References

No definition available.

+ Details

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

- Definition

Equity Method Investment, Put or Call Period

+ References

No definition available.

+ Details

Name:	cmcsa_EquityMethodInvestmentPutorCallPeriod
Namespace Prefix:	cmcsa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the entity's proportionate share for the period of a goodwill impairment charge recorded by its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. The amount is recorded in equity in net income (losses) of investees, net.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of any residual returns that Comcast has the right to receive

+ References

No definition available.

+ Details

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

- Definition

Pretax gain recognized as a result of the sale of The Weather Channel's product and technology business to IBM

+ References

No definition available.

+ Details

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

- Definition

Term of agreement for Atairos

+ References

No definition available.

+ Details

Name:	cmcsa_TermOfAgreement
Namespace Prefix:	cmcsa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

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

- Definition

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 3: 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=66902209&loc=d3e3602-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66022249&loc=d3e33749-111570

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=cmcsa_AtairosMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_TitleOfIndividualAxis=cmcsa_FormerCFOMember
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Data Type:	na
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- Details

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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Data Type:	na
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- Details

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Investments (Equity Method Investments) (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity in net losses of investees			$ 104	$ 325	$ (97)
NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity in net losses of investees			$ 99	376	(46)
Atairos [Member]
Schedule of Equity Method Investments [Line Items]
Term of agreement			12 years
Funding commitment			$ 4,000
Management fee funding commitment			$ 40
Percent of losses			99.00%
Percentage of residual returns			86.50%
Purchases of investments			$ 1,200
Capital Contribution to VIE accrued but not yet paid			447
Atairos [Member] \| Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Funding commitment by management company investors			100
Atairos [Member] \| Former CFO [Member] \| Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Funding commitment by management company investors			40
Hulu [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	30.00%					33.00%
Put/Call Period	3 years
Deferred gain	$ 159
Equity in net losses of investees			168	106	20
Hulu [Member] \| NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	30.00%					33.00%
Put/Call Period	3 years
Deferred gain	$ 159
Equity in net losses of investees			$ 168	106	$ 20
The Weather Channel [Member]
Schedule of Equity Method Investments [Line Items]
Pretax gain on sale of investment		$ 108
Goodwill impairment loss from equity method investments				333
The Weather Channel [Member] \| NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Pretax gain on sale of investment		$ 108
Goodwill impairment loss from equity method investments				$ 333
Time Warner, Inc. [Member] \| Hulu [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	10.00%
Time Warner, Inc. [Member] \| Hulu [Member] \| NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	10.00%