v2.4.1.9

Condensed Consolidating Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Operating Activities |  |  |
Net cash provided by (used in) operating activities | $ 16,945,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities | $ 14,160,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities | $ 14,854,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities
Investing Activities |  |  |
Capital expenditures | (7,420,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment | (6,596,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment | (5,714,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Cash paid for intangible assets | (1,122,000,000)us-gaap_PaymentsToAcquireIntangibleAssets | (1,009,000,000)us-gaap_PaymentsToAcquireIntangibleAssets | (923,000,000)us-gaap_PaymentsToAcquireIntangibleAssets
Acquisitions and construction of real estate properties | (43,000,000)cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties | (1,904,000,000)cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties
Acquisitions, net of cash acquired | (477,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired | (99,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired | (90,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
Proceeds from sales of businesses and investments | 666,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments | 1,083,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments | 3,102,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments
Return of capital from investees | 25,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital | 149,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital | 2,362,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital
Purchases of investments | (191,000,000)us-gaap_PaymentsToAcquireInvestments | (1,223,000,000)us-gaap_PaymentsToAcquireInvestments | (297,000,000)us-gaap_PaymentsToAcquireInvestments
Other | (171,000,000)us-gaap_PaymentsForProceedsFromOtherInvestingActivities | 85,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities | 74,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities
Net cash provided by (used in) investing activities | (8,733,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities | (9,514,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities | (1,486,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | (504,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt | 1,345,000,000 us-gaap_ProceedsFromRepaymentsOfShortTermDebt | (544,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt
Proceeds from borrowings | 4,182,000,000 us-gaap_ProceedsFromOtherDebt | 2,933,000,000 us-gaap_ProceedsFromOtherDebt | 4,544,000,000 us-gaap_ProceedsFromOtherDebt
Repurchases and repayments of debt | (3,175,000,000)us-gaap_RepaymentsOfOtherDebt | (2,444,000,000)us-gaap_RepaymentsOfOtherDebt | (2,881,000,000)us-gaap_RepaymentsOfOtherDebt
Repurchases and retirements of common stock | (4,251,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock | (2,000,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock | (3,000,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock
Dividends paid | (2,254,000,000)us-gaap_PaymentsOfDividends | (1,964,000,000)us-gaap_PaymentsOfDividends | (1,608,000,000)us-gaap_PaymentsOfDividends
Issuances of common stock | 35,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock | 40,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock | 233,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock
Purchase of NBCUniversal noncontrolling common equity interest | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries | (10,761,000,000)us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | (220,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock | (215,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock | (691,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock
Settlement of Station Venture liability | 0 cmcsa_SettlementOfStationVentureLiability | (602,000,000)cmcsa_SettlementOfStationVentureLiability | 0 cmcsa_SettlementOfStationVentureLiability
Other | 167,000,000 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities | (211,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities | (90,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
Net cash provided by (used in) financing activities | (6,020,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities | (13,879,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities | (4,037,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities
Increase (decrease) in cash and cash equivalents | 2,192,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease | (9,233,000,000)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease | 9,331,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
Cash and cash equivalents, beginning of year | 1,718,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue | 10,951,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue | 1,620,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue
Cash and cash equivalents, end of year | 3,910,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue | 1,718,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue | 10,951,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue
Elimination and Consolidation Adjustments [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | 0 us-gaap_NetCashProvidedByUsedInOperatingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInOperatingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInOperatingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Investing Activities |  |  |
Net transactions with affiliates | 0 cmcsa_NetTransactionsWithAffiliates / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_NetTransactionsWithAffiliates / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_NetTransactionsWithAffiliates / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Capital expenditures | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Cash paid for intangible assets | 0 us-gaap_PaymentsToAcquireIntangibleAssets / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Proceeds from sales of businesses and investments | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Return of capital from investees | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Purchases of investments | 0 us-gaap_PaymentsToAcquireInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsToAcquireInvestments / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Other | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Net cash provided by (used in) investing activities | 0 us-gaap_NetCashProvidedByUsedInInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInInvestingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Proceeds from borrowings | 0 us-gaap_ProceedsFromOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Repurchases and repayments of debt | 0 us-gaap_RepaymentsOfOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_RepaymentsOfOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_RepaymentsOfOtherDebt / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsOfDividends / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_PaymentsOfDividends / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Purchase of NBCUniversal noncontrolling common equity interest |  | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember |
Other | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Net cash provided by (used in) financing activities | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Increase (decrease) in cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Cash and cash equivalents, beginning of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Cash and cash equivalents, end of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_ConsolidationItemsAxis = cmcsa_EliminationAndConsolidationAdjustmentsMember
Comcast Parent [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | (354,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (600,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (362,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investing Activities |  |  |
Net transactions with affiliates | 4,784,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 66,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 3,845,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Capital expenditures | (3,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (7,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (10,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Cash paid for intangible assets | (6,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (4,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (6,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Proceeds from sales of businesses and investments | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Return of capital from investees | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Purchases of investments | (19,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (11,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Net cash provided by (used in) investing activities | 4,756,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 44,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 3,829,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | (1,350,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,349,000,000 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (1,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Proceeds from borrowings | 4,180,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 2,933,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 2,536,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Repurchases and repayments of debt | (1,000,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (1,726,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Repurchases and retirements of common stock | (4,251,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (2,000,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (3,000,000,000)us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Dividends paid | (2,254,000,000)us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (1,964,000,000)us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (1,608,000,000)us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Issuances of common stock | 35,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 40,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 233,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Purchase of NBCUniversal noncontrolling common equity interest |  | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Other | 238,000,000 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 198,000,000 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 99,000,000 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Net cash provided by (used in) financing activities | (4,402,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 556,000,000 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (3,467,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Increase (decrease) in cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Cash and cash equivalents, beginning of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Cash and cash equivalents, end of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Comcast Holdings [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | 9,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | (3,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | (7,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Investing Activities |  |  |
Net transactions with affiliates | (9,000,000)cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 3,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 206,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Capital expenditures | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Cash paid for intangible assets | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Proceeds from sales of businesses and investments | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Return of capital from investees | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Purchases of investments | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Other | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 3,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Net cash provided by (used in) investing activities | (9,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 3,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 209,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Proceeds from borrowings | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Repurchases and repayments of debt | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | (202,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Purchase of NBCUniversal noncontrolling common equity interest |  | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember |
Other | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Net cash provided by (used in) financing activities | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | (202,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Increase (decrease) in cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Cash and cash equivalents, beginning of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
Cash and cash equivalents, end of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastHoldingsMember
CCCL Parent [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | (57,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | (151,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | (177,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember
Investing Activities |  |  |
Net transactions with affiliates | 57,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CcclParentMember | 2,248,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CcclParentMember | 177,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CcclParentMember
Capital expenditures | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CcclParentMember
Cash paid for intangible assets | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CcclParentMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_CcclParentMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CcclParentMember
Proceeds from sales of businesses and investments | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember
Return of capital from investees | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CcclParentMember
Purchases of investments | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CcclParentMember
Other | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember
Net cash provided by (used in) investing activities | 57,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 2,248,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 177,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember
Proceeds from borrowings | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember
Repurchases and repayments of debt | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | (2,097,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CcclParentMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CcclParentMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CcclParentMember
Purchase of NBCUniversal noncontrolling common equity interest |  | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_CcclParentMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CcclParentMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_CcclParentMember |
Other | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember
Net cash provided by (used in) financing activities | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | (2,097,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CcclParentMember
Increase (decrease) in cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CcclParentMember
Cash and cash equivalents, beginning of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember
Cash and cash equivalents, end of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CcclParentMember
Combined CCHMO Parents [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | (82,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (94,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (114,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Investing Activities |  |  |
Net transactions with affiliates | 82,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 332,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 667,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Capital expenditures | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Cash paid for intangible assets | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Proceeds from sales of businesses and investments | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Return of capital from investees | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Purchases of investments | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Other | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Net cash provided by (used in) investing activities | 82,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 332,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 667,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Proceeds from borrowings | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Repurchases and repayments of debt | 0 us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (238,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (553,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Purchase of NBCUniversal noncontrolling common equity interest |  | 0 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember |
Other | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Net cash provided by (used in) financing activities | 0 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (238,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | (553,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Increase (decrease) in cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Cash and cash equivalents, beginning of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
Cash and cash equivalents, end of year | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember | 0 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_CombinedCchmoParentsMember
NBCUniversal Media Parent [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | (1,299,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (1,102,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (1,347,000,000)us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Investing Activities |  |  |
Net transactions with affiliates | 2,247,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (470,000,000)cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 4,850,000,000 cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Capital expenditures | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Cash paid for intangible assets | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Acquisitions and construction of real estate properties | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember |
Acquisitions, net of cash acquired | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Proceeds from sales of businesses and investments | 8,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 2,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Return of capital from investees | 1,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 128,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Purchases of investments | (10,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (3,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (19,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Other | 4,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (20,000,000)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (22,000,000)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Net cash provided by (used in) investing activities | 2,250,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (363,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 4,809,000,000 us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (550,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Proceeds from borrowings | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 1,995,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Repurchases and repayments of debt | (902,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (88,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (2,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Purchase of NBCUniversal noncontrolling common equity interest |  | (3,200,000,000)us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 0 cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Settlement of Station Venture liability |  | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember |
Other | 0 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (40,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (14,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Net cash provided by (used in) financing activities | (902,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (3,328,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 1,429,000,000 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Increase (decrease) in cash and cash equivalents | 49,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | (4,793,000,000)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 4,891,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Cash and cash equivalents, beginning of year | 336,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 5,129,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 238,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Cash and cash equivalents, end of year | 385,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 336,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember | 5,129,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_NbcuniversalMediaParentMember
Comcast Non-Guarantor Subsidiaries [Member] |  |  |
Operating Activities |  |  |
Net cash provided by (used in) operating activities | 18,728,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 16,110,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 16,861,000,000 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Investing Activities |  |  |
Net transactions with affiliates | (7,161,000,000)cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (2,179,000,000)cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (9,745,000,000)cmcsa_NetTransactionsWithAffiliates / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Capital expenditures | (7,417,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (6,589,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (5,704,000,000)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Cash paid for intangible assets | (1,116,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (1,005,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (917,000,000)us-gaap_PaymentsToAcquireIntangibleAssets / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Acquisitions and construction of real estate properties | (43,000,000)cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (1,904,000,000)cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember |
Acquisitions, net of cash acquired | (477,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (99,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (90,000,000)us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Proceeds from sales of businesses and investments | 658,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 1,081,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 3,102,000,000 cmcsa_ProceedsFromSalesOfBusinessesAndInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Return of capital from investees | 24,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 21,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 2,362,000,000 us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Purchases of investments | (162,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (1,209,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (278,000,000)us-gaap_PaymentsToAcquireInvestments / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Other | (175,000,000)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 105,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 93,000,000 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Net cash provided by (used in) investing activities | (15,869,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (11,778,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (11,177,000,000)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Financing Activities |  |  |
Proceeds from (repayments of) short-term borrowings, net | 846,000,000 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (4,000,000)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 7,000,000 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Proceeds from borrowings | 2,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 13,000,000 us-gaap_ProceedsFromOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Repurchases and repayments of debt | (1,273,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (21,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (398,000,000)us-gaap_RepaymentsOfOtherDebt / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Repurchases and retirements of common stock | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_PaymentsForRepurchaseOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Dividends paid | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_PaymentsOfDividends / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Issuances of common stock | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 0 us-gaap_ProceedsFromIssuanceOfCommonStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Purchase of NBCUniversal noncontrolling common equity interest |  | (7,561,000,000)us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember |
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock | (220,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (215,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (691,000,000)cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Settlement of Station Venture liability |  | (602,000,000)cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember |
Other | (71,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (369,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (175,000,000)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Net cash provided by (used in) financing activities | (716,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (8,772,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (1,244,000,000)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Increase (decrease) in cash and cash equivalents | 2,143,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | (4,440,000,000)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 4,440,000,000 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Cash and cash equivalents, beginning of year | 1,382,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 5,822,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | 1,382,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember
Cash and cash equivalents, end of year | $ 3,525,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | $ 1,382,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember | $ 5,822,000,000 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = cmcsa_ComcastNonGuarantorSubsidiariesMember

X
- Definition Decrease in noncontrolling interest balance from payment of dividends or other distributions by the non-wholly owned subsidiary or partially owned entity, included in the consolidation of the parent entity, to the noncontrolling interest holders and dividends for redeemable subsidiary preferred stock. + References No definition available. + Details
Name: | cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Net transactions with affiliates. + References No definition available. + Details
Name: | cmcsa_NetTransactionsWithAffiliates
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow for the acquisition and construction of buildings (properties) whether for investment or use. + References No definition available. + Details
Name: | cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow associated with the sale of businesses and investments during the period. + References No definition available. + Details
Name: | cmcsa_ProceedsFromSalesOfBusinessesAndInvestments
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow associated with the settlement of the Station Venture liability. + References No definition available. + Details
Name: | cmcsa_SettlementOfStationVentureLiability
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3044-108585 + Details
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