v2.4.0.8

Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 6 Months Ended
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Jun. 30, 2014
Number of stock options granted | 16.4
Number of restricted share units granted | 5.4
Weighted average fair value of stock options granted | $ 11.09
Weighed average fair value of restricted share units granted | $ 46.57
Stock Options [Member] |
Unrecognized pretax compensation expense on nonvested awards | $ 392
Restricted Share Units [Member] |
Unrecognized pretax compensation expense on nonvested awards | $ 529

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