v2.4.1.9

Business and Basis of Presentation (Details) | Dec. 31, 2014 numberofcustomers | Mar. 19, 2013
--- | --- | ---
Remaining equity interest acquired |  | 49.00%cmcsa_NoncontrollingInterestAcquired
Total customer relationships | 27,000,000 cmcsa_Totalcustomerrelationships |
NBCUniversal Media, LLC [Member] |  |
Remaining equity interest acquired |  | 49.00%cmcsa_NoncontrollingInterestAcquired / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Video Customers [Member] |  |
Number of customers | 22,400,000 cmcsa_NumberOfCustomers / us-gaap_StatementBusinessSegmentsAxis = cmcsa_VideoCustomersMember |
High-speed Internet Customers [Member] |  |
Number of customers | 22,000,000 cmcsa_NumberOfCustomers / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HighSpeedInternetCustomersMember |
Voice Customers [Member] |  |
Number of customers | 11,200,000 cmcsa_NumberOfCustomers / us-gaap_StatementBusinessSegmentsAxis = cmcsa_PhoneCustomersMember |

X
- Definition Represents the percentage of voting interest acquired at the acquisition date from a noncontrolling interest. + References No definition available. + Details
Name: | cmcsa_NoncontrollingInterestAcquired
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of customers + References No definition available. + Details
Name: | cmcsa_NumberOfCustomers
Namespace Prefix: | cmcsa_
Data Type: | xbrli:positiveIntegerItemType
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: | dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
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_PhoneCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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