Long-Term Debt (Narrative) (Details) $ in Millions	Mar. 31, 2017 USD ($)
Debt Instrument [Line Items]
Total debt	$ 61,800
Fair value of debt	66,700
Amounts available under revolving credit facilities	7,400
NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Total debt	11,700
Fair value of debt	$ 12,600
Ownership in cable holding company subsidiaries	100.00%
NBCUniversal Enterprise [Member] \| NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Related party aggregate principal amount senior notes not subject to guarantee	$ 3,300
Related party credit facility not subject to guarantee	1,500
Related party liquidation preference preferred stock not subject to guarantee	725
Comcast Revolving Credit Facility [Member] \| NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	7,000
Comcast and CCCL Parent Debt Securities [Member] \| NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	45,500
NBCUniversal Enterprise Credit Facility [Member]
Debt Instrument [Line Items]
Amounts available under revolving credit facilities	585
Commercial Paper [Member]
Debt Instrument [Line Items]
Commercial paper	0
NBCUniversal Enterprise Commercial Paper [Member]
Debt Instrument [Line Items]
Commercial paper	915
Universal Studios Japan Term Loans [Member]
Debt Instrument [Line Items]
Non Guarantee Obligations Current Principal Balance	3,400
Universal Studios Japan Term Loans [Member] \| NBCUniversal Media LLC [Member]
Debt Instrument [Line Items]
Non Guarantee Obligations Current Principal Balance	$ 3,400

Principal amount of debt securities subject to guarantee.

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Principal amount of debt instruments not guaranteed by Comcast Corporation, the cable guarantors nor NBCUniversal Media, LLC.

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Represents the Company's ownership in its cable holding company subsidiaries.

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Represents the related party aggregate principal amount of senior notes not subject to guarantee by NBCUniversal.

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Represents the related party credit facility not subject to guarantee by NBCUniversal.

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Represents the related party liquidation preference of preferred stock not subject to guarantee by NBCUniversal.

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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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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.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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