v2.4.1.9

Share-Based Compensation (Recognized Share-Based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Recognized share-based compensation expense | $ 414 us-gaap_AllocatedShareBasedCompensationExpense | $ 334 us-gaap_AllocatedShareBasedCompensationExpense | $ 301 us-gaap_AllocatedShareBasedCompensationExpense
NBCUniversal Media, LLC [Member] |  |  |
Recognized share-based compensation expense | 91 us-gaap_AllocatedShareBasedCompensationExpense / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 62 us-gaap_AllocatedShareBasedCompensationExpense / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 47 us-gaap_AllocatedShareBasedCompensationExpense / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Stock Options [Member] |  |  |
Recognized share-based compensation expense | 160 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember | 139 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember | 131 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember
Stock Options [Member] | NBCUniversal Media, LLC [Member] |  |  |
Recognized share-based compensation expense | 16 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 15 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 15 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Restricted Share Units [Member] |  |  |
Recognized share-based compensation expense | 231 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember | 175 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember | 154 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember
Restricted Share Units [Member] | NBCUniversal Media, LLC [Member] |  |  |
Recognized share-based compensation expense | 69 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 42 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 28 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Employee Stock Purchase Plan [Member] |  |  |
Recognized share-based compensation expense | 23 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember | 20 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember | 16 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember
Employee Stock Purchase Plan [Member] | NBCUniversal Media, LLC [Member] |  |  |
Recognized share-based compensation expense | $ 6 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 5 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 4 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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