v2.4.1.9

Equity (Changes in Common Stock) (Details) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Repurchases and retirements of common stock | 81,000,000 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares | 49,000,000 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares | 96,000,000 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Class A Common Stock [Member] |  |  |
Common Stock, Shares, Outstanding, Beginning Balance | 2,138,075,133 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 2,122,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 2,095,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Stock compensation plans | 13,000,000 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 14,000,000 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 24,000,000 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Repurchases and retirements of common stock | (22,000,000)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Employee stock purchase plan | 2,000,000 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 2,000,000 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 3,000,000 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Common Stock, Shares, Outstanding, Ending Balance | 2,131,137,862 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 2,138,075,133 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember | 2,122,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Class A Special Common Stock [Member] |  |  |
Common Stock, Shares, Outstanding, Beginning Balance | 459,030,180 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 508,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 601,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Stock compensation plans | 0 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 0 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 3,000,000 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Repurchases and retirements of common stock | (59,000,000)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | (49,000,000)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | (96,000,000)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Employee stock purchase plan | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Common Stock, Shares, Outstanding, Ending Balance | 400,484,837 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 459,030,180 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember | 508,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Class B Common Stock [Member] |  |  |
Common Stock, Shares, Outstanding, Beginning Balance | 9,444,375 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 9,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 9,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Stock compensation plans | 0 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Repurchases and retirements of common stock | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Employee stock purchase plan | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 0 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Common Stock, Shares, Outstanding, Ending Balance | 9,444,375 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 9,444,375 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember | 9,000,000 us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember

X
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