v2.4.1.9

Share-Based Compensation (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income tax effects allocated directly to equity, other | $ 299 us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquityOther | $ 244 us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquityOther | $ 164 us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquityOther
Share-based compensation arrangement by share-based payment award, award vesting period in years | 5 years 0 months 0 days |  |
NBCUniversal Media, LLC [Member] |  |  |
Share-based compensation arrangement by share-based payment award, award vesting period in years | 5 years 0 months 0 days |  |
Stock Options [Member] |  |  |
Unrecognized pretax compensation expense on nonvested awards | 321 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember |  |
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years) | 1 year 9 months 18 days |  |
Period from grant date that an equity-based award expires | 10 years 0 months 0 days |  |
Stock Options [Member] | NBCUniversal Media, LLC [Member] |  |  |
Unrecognized pretax compensation expense on nonvested awards | 25 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |  |
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years) | 2 years 1 month 6 days |  |
Period from grant date that an equity-based award expires | 10 years 0 months 0 days |  |
Restricted Share Units [Member] |  |  |
Unrecognized pretax compensation expense on nonvested awards | 505 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember |  |
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years) | 1 year 8 months 12 days |  |
Restricted Share Units [Member] | NBCUniversal Media, LLC [Member] |  |  |
Unrecognized pretax compensation expense on nonvested awards | $ 124 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |  |
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years) | 1 year 7 months 6 days |  |

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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The tax effect of items occurring during the period that have been charged or credited directly to components of shareholders' equity and are not otherwise defined. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 20 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=18498875&loc=d3e39076-109324 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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