v2.4.0.6

Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 | Jun. 30, 2011
Number of stock options granted |  |  | 21.8 |
Number of restricted share units granted |  |  | 5.7 |
Weighted average fair value of stock options granted |  |  | $ 7.38 |
Fair value of restricted share units granted |  |  | $ 27.43 |
Employee Payroll Deductions For Share Purchases Through Employee Stock Purchase Plan | $ 18 | $ 13 | $ 36 | $ 28
Stock Options [Member] |  |  |  |
Unrecognized pretax compensation expense on nonvested awards | 385 |  | 385 |
Restricted Share Units [Member] |  |  |  |
Unrecognized pretax compensation expense on nonvested awards | $ 411 |  | $ 411 |

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- Definition Aggregate amount of payroll deductions that were used to satisfy employees' share purchases under our Employee Stock Purchase Plans. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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

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- Definition As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph h -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: 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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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant