XML 41 R49.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Basis of Presentation and Summary of Significant Accounting Policies (Details) | 12 Months Ended
--- | ---
Dec. 31, 2019 business segment
Business And Basis Of Presentation [Line Items] |
Number of primary businesses | business | 3
NBCUniversal Media LLC [Member] |
Business And Basis Of Presentation [Line Items] |
Number of reportable segments | 4
Cable Communications [Member] |
Business And Basis Of Presentation [Line Items] |
Number of reportable segments | 1
NBCUniversal Segments [Member] |
Business And Basis Of Presentation [Line Items] |
Number of reportable segments | 4
Sky Limited [Member] |
Business And Basis Of Presentation [Line Items] |
Number of reportable segments | 1

X
- Definition Business And Basis Of Presentation + References No definition available. + Details
Name: | cmcsa_BusinessAndBasisOfPresentationLineItems
Namespace Prefix: | cmcsa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number Of Businesses + References No definition available. + Details
Name: | cmcsa_NumberOfBusinesses
Namespace Prefix: | cmcsa_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=cmcsa_CableCommunicationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=cmcsa_NBCUniversalSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=cmcsa_SkyLimitedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |