v2.4.1.9

Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015
Number of stock options granted | 17.6 cmcsa_StockOptionsGranted
Number of restricted share units granted | 5.1 cmcsa_RestrictedShareUnitsGranted
Weighted average fair value of stock options granted | $ 11.79 cmcsa_FairValueOfStockOptionsGranted
Weighted average fair value of restricted share units granted | $ 59.5 cmcsa_FairValueOfRestrictedShareUnitsGranted
Stock Options [Member] |
Unrecognized pretax compensation expense on nonvested awards | $ 461 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember
Restricted Share Units [Member] |
Unrecognized pretax compensation expense on nonvested awards | $ 725 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember

X
- Definition The weighted average fair value of restricted share units granted related to our annual management grant program. + References No definition available. + Details
Name: | cmcsa_FairValueOfRestrictedShareUnitsGranted
Namespace Prefix: | cmcsa_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The weighted average fair value of stock options granted related to our annual management grant program. + References No definition available. + Details
Name: | cmcsa_FairValueOfStockOptionsGranted
Namespace Prefix: | cmcsa_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of restricted share units granted related to our annual management grant program. + References No definition available. + Details
Name: | cmcsa_RestrictedShareUnitsGranted
Namespace Prefix: | cmcsa_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of stock options granted related to our annual management grant program. + References No definition available. + Details
Name: | cmcsa_StockOptionsGranted
Namespace Prefix: | cmcsa_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=us-gaap_RestrictedStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |