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Long-Term Debt (Cross-Guarantee Structure) (Details) - NBCUniversal Media LLC [Member] $ in Millions | Jun. 30, 2018 USD ($)
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Debt Instrument [Line Items] |
Ownership in cable holding company subsidiaries | 100.00%
NBCUniversal Enterprise [Member] |
Debt Instrument [Line Items] |
Related party aggregate principal amount senior notes not subject to guarantee | $ 3,000
Related party credit facility not subject to guarantee | 1,500
Related party liquidation preference preferred stock not subject to guarantee | 725
Comcast and Comcast Cable Debt Securities [Member] |
Debt Instrument [Line Items] |
Principal amount of debt securities subject to guarantee | 50,300
Revolving Credit Facility [Member] |
Debt Instrument [Line Items] |
Guarantee obligations, maximum capacity | $ 7,000

X
- Definition Principal amount of debt securities subject to guarantee. + References No definition available. + Details
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Balance Type: | credit
Period Type: | instant

X
- Definition Maximum capacity of credit facility subject to cross-guarantee + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the Company's ownership in its cable holding company subsidiaries. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the related party aggregate principal amount of senior notes not subject to guarantee by NBCUniversal. + 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 Represents the related party credit facility not subject to guarantee by NBCUniversal. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the related party liquidation preference of preferred stock not subject to guarantee by NBCUniversal. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

X
- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |