Principal amount of debt securities subject to guarantee.

No definition available.

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Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum capacity of credit facility subject to cross-guarantee

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Guarantee Obligations, Term Loans

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Term loans not guaranteed by Comcast Corporation, the cable guarantors nor NBCUniversal Media, LLC.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- 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

- 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

- 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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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmcsa_UniversalStudiosJapanTermLoanMaturingMarch2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
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- Details

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Data Type:	na
Balance Type:
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- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Long-Term Debt (Guarantee Structure) (Details) $ in Millions, ¥ in Billions, ¥ in Billions	Mar. 31, 2019 JPY (¥)	Mar. 31, 2019 CNY (¥)	Mar. 31, 2019 USD ($)
Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee			$ 92,300
NBCUniversal Enterprise Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee			3,000
Universal Studios Japan Term Loan Maturing March 2022 [Member]
Debt Instrument [Line Items]
Guarantee obligations, term loans	¥ 385		3,500
Universal Beijing Resort Term Loans [Member]
Debt Instrument [Line Items]
Principal amount of debt securities not subject to guarantee		¥ 5.5	815
Sky Outstanding Indebtedness [Member]
Debt Instrument [Line Items]
Principal amount of debt securities not subject to guarantee			$ 10,000
NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Ownership in cable holding company subsidiaries	100.00%	100.00%	100.00%
NBCUniversal Media LLC [Member] \| NBCUniversal Enterprise [Member]
Debt Instrument [Line Items]
Related party aggregate principal amount senior notes not subject to guarantee			$ 3,000
Related party liquidation preference preferred stock not subject to guarantee			725
NBCUniversal Media LLC [Member] \| Comcast and Comcast Cable Debt Securities [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee			84,600
NBCUniversal Media LLC [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Guarantee obligations, maximum capacity of credit facility			$ 7,600