v3.3.1.900

Business and Basis of Presentation (Details) - numberofcustomers numberofcustomers in Millions | Dec. 31, 2015 | Nov. 13, 2015
--- | --- | ---
Total Customer Relationships | 27.7 |
Video Customers [Member] |  |
Number of customers | 22.3 |
High-speed Internet Customers [Member] |  |
Number of customers | 23.3 |
Voice Customers [Member] |  |
Number of customers | 11.5 |
Universal Studios Japan [Member] |  |
Ownership Percentage |  | 51.00%
Universal Studios Japan [Member] | NBCUniversal Media LLC [Member] |  |
Ownership Percentage |  | 51.00%

X
- Definition Represents the number of customers that subscribe to our services. + References No definition available. + Details
Name: | cmcsa_NumberOfCustomers
Namespace Prefix: | cmcsa_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage + References No definition available. + Details
Name: | cmcsa_OwnershipPercentageInNewCompany
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of residential and business customers that subscribe to at least one of our three primary services of video, high-speed Internet and voice. + References No definition available. + Details
Name: | cmcsa_Totalcustomerrelationships
Namespace Prefix: | cmcsa_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

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

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

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=cmcsa_UniversalStudiosJapanMember
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: |