v2.4.1.9

Supplemental Financial Information (Noncash Investing and Financing Activities)(Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 19, 2013
Noncontrolling Interest Acquired				49.00%cmcsa_NoncontrollingInterestAcquired
Purchase of NBCUniversal noncontrolling interest		$ 16,700,000,000cmcsa_ConsiderationTransferredToAcquireAdditionalInterestInSubsidiaries
Consideration transferred related to the Redemption Transaction and purchase of certain properties		725,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource
Total noncash consideration transferred related to the Redemption Transaction		6,000,000,000cmcsa_TotalNoncashConsiderationTransferredInRedemptionTransaction
Dividends payable, amount	572,000,000us-gaap_DividendsPayableCurrentAndNoncurrent	509,000,000us-gaap_DividendsPayableCurrentAndNoncurrent	430,000,000us-gaap_DividendsPayableCurrentAndNoncurrent
Dividends payable, amount per share	$ 0.225us-gaap_DividendsPayableAmountPerShare	$ 0.195us-gaap_DividendsPayableAmountPerShare	$ 0.1625us-gaap_DividendsPayableAmountPerShare
Capital expenditures incurred but not yet paid	797,000,000us-gaap_CapitalExpendituresIncurredButNotYetPaid	872,000,000us-gaap_CapitalExpendituresIncurredButNotYetPaid	757,000,000us-gaap_CapitalExpendituresIncurredButNotYetPaid
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			85,000,000us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1
Fair Value Equity Securities Settlement	3,200,000,000cmcsa_FairValueEquitySecuritiesSettlement	1,400,000,000cmcsa_FairValueEquitySecuritiesSettlement
NBCUniversal Media, LLC [Member]
Capital expenditures incurred but not yet paid	148,000,000us-gaap_CapitalExpendituresIncurredButNotYetPaid / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember	306,000,000us-gaap_CapitalExpendituresIncurredButNotYetPaid / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			85,000,000us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1 / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember
Revolving Credit Facility Member
Consideration transferred related to the Redemption Transaction and purchase of certain properties		1,250,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / dei_LegalEntityAxis = us-gaap_RevolvingCreditFacilityMember
NBCUniversal Enterprise Senior Unsecured Debt Securities [Member]
Consideration transferred related to the Redemption Transaction and purchase of certain properties		4,000,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / dei_LegalEntityAxis = us-gaap_SeniorNotesMember
NBCUniversal Enterprise Preferred Stock [Member]
Consideration transferred related to the Redemption Transaction and purchase of certain properties		$ 725,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / dei_LegalEntityAxis = us-gaap_PreferredStockMember

X

- Definition

The consideration associated with the purchase of GE's 49% noncontrolling common equity interest in NBCUniversal related to the Redemption Transaction and the acquisition of certain properties at 30 Rockefeller Plaza and Engelwood Cliffs.

+ References

No definition available.

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- Definition

The total consideration associated with the purchase of GE's 49% noncontrolling common equity interest in NBCUniversal.

+ References

No definition available.

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- Definition

Fair value method equity securities used to settle our obligations under prepaid forward sale agreements in the period.

+ References

No definition available.

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- Definition

Represents the percentage of voting interest acquired at the acquisition date from a noncontrolling interest.

+ References

No definition available.

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X

- Definition

The total noncash consideration transferred related to the Redemption Transaction.

+ References

No definition available.

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- Definition

Future cash outflow to pay for purchases of fixed assets that have occurred.

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-SubTopic 10

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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