v3.3.1.900

Investments (Cost Method Investments) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014
Vox Media [Member] |  |
Cost Method Investments,Original Cost | $ 200 |
Vox Media [Member] | NBCUniversal Media LLC [Member] |  |
Cost Method Investments,Original Cost | 200 |
BuzzFeed [Member] |  |
Cost Method Investments,Original Cost | 200 |
BuzzFeed [Member] | NBCUniversal Media LLC [Member] |  |
Cost Method Investments,Original Cost | 200 |
Air Touch [Member] |  |
Fair value of AirTouch preferred stock related to redeemable preferred shares | 1,700 | $ 1,700
Aggregate redemption value | 1,750 |
Carrying amount of redeemable preferred stock | 1,600 | 1,600
Fair value of redeemable preferred shares | 1,700 | 1,700
Nonredeemable preferred stock | 100 | $ 100
Preferred Shares Redeemable in April 2020 [Member] |  |
Aggregate redemption value | $ 1,650 |

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- Definition Carrying amount of redeemable preferred stock + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Fair value of our redeemable subsidiary preferred shares and/or stock + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The fair value of a cost method investment related to redeemable preferred shares. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Nonredeemable preferred stock issued by a wholly owned subsidiary of the company. + References No definition available. + Details
Name: | cmcsa_NonredeemablePreferredStock
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Preferred stock aggregate redemption value + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Original amount of cost-method investments at the acquisition date. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | cmcsa_LegalEntity1Axis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | dei_LegalEntityAxis=cmcsa_PreferredSharesRedeemableInApril2020Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |