v3.7.0.1

Significant Transactions Schedule of FCC Spectrum Auction (Details) - Subsequent Event [Member] - FCC Spectrum Auction [Member] $ in Millions	Apr. 13, 2017 USD ($)
FCC Spectrum Auction [Line Items]
Expected Proceeds From Spectrum Auction	$ 482
Assets Held-for-sale, Not Part of Disposal Group, Current, Other	144
Amount to acquire broadcast spectrum	1,700
Deposit To Acquire Intangible Asset	1,800
NBCUniversal Media LLC [Member]
FCC Spectrum Auction [Line Items]
Expected Proceeds From Spectrum Auction	482
Assets Held-for-sale, Not Part of Disposal Group, Current, Other	$ 144

X

- Definition

Amount agreed upon to acquire broadcast spectrum in a future period.

+ References

No definition available.

+ Details

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

X

- Definition

Deposit paid in a prior period for the right to an intangible asset in a future period.

+ References

No definition available.

+ Details

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

X

- Definition

Amount represents the expected proceeds upon the completion of the sale of spectrum in connection with the FCC spectrum auction.

+ References

No definition available.

+ Details

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

X

- Definition

FCC Spectrum Auction [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	cmcsa_
Data Type:	xbrli:stringItemType
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X

- Definition

Amount of other assets held-for-sale that are not part of a disposal group, expected to be sold within a year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 15
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6390208&loc=d3e400-110220

+ Details

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X

- Details

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Namespace Prefix:
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Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Period Type: