XML 112 R74.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Significant Transactions (FCC Spectrum Auction) (Details) - FCC Spectrum [Member] - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jul. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2019 | Dec. 31, 2018 | Jun. 30, 2017
FCC Spectrum Auction [Line Items] |  |  |  |  |  |
Proceeds from FCC spectrum auction | $ 482 |  |  |  |  |
Gain on sale of spectrum rights |  | $ 337 |  |  |  |
Amount of spectrum acquired |  |  |  | $ 2,337 | $ 2,333 | $ 1,700
Deposit to acquire intangible asset |  |  | $ 1,800 |  |  |
NBCUniversal Media LLC [Member] |  |  |  |  |  |
FCC Spectrum Auction [Line Items] |  |  |  |  |  |
Proceeds from FCC spectrum auction | $ 482 |  |  |  |  |
Gain on sale of spectrum rights |  | $ 337 |  |  |  |
Amount of spectrum acquired |  |  |  | $ 612 | $ 608 |

X
- Definition Deposit paid in a prior period for the right to an intangible asset in a future period. + References No definition available. + Details
Name: | cmcsa_DepositToAcquireIntangibleAsset
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition FCC Spectrum Auction [Line Items] + References No definition available. + Details
Name: | cmcsa_FCCSpectrumAuctionLineItems
Namespace Prefix: | cmcsa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of gain (loss) on sale or disposal of intangible assets. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnDispositionOfIntangibleAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash inflow from disposal of asset without physical form usually arising from contractual or other legal rights, excluding goodwill. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfIntangibleAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LicensingAgreementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |