v2.4.0.8

Significant Transactions (Narrative) (Details) | Sep. 30, 2014
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Significant Transactions [Line Items] |
Company Shares Exchanged For Each Acquiree Share | 2.875
Acquiree Stockholders Percentage Ownership In Parent Company | 24.00%
Merger Agreement Undertaking Number Of Divested Customers [Member] |
Significant Transactions [Line Items] |
Number of customers | 3,000,000
Divestiture Transactions Net Disposition Of Customers [Member] |
Significant Transactions [Line Items] |
Number of customers | 3,900,000
Divestiture Transactions Customers To Be Spun Off In SpinCo [Member] |
Significant Transactions [Line Items] |
Number of customers | 2,500,000
Divestiture Transactions Like Kind Divestiture Of Time Warner Cable Customers [Member] |
Significant Transactions [Line Items] |
Number of customers | 1,500,000
Divestiture Transactions Like Kind Receipt Of Charter Communications Customers [Member] |
Significant Transactions [Line Items] |
Number of customers | 1,700,000
Divestiture Transactions Sale Of Time Warner Cable Customers [Member] |
Significant Transactions [Line Items] |
Number of customers | 1,500,000
Comcast Corporate Shareholders [Member] |
Significant Transactions [Line Items] |
Ownership Percentage In SpinCo | 67.00%
Ownership Percentage In New Charter | 10.00%
New Charter [Member] |
Significant Transactions [Line Items] |
Ownership Percentage In SpinCo | 33.00%

X
- Definition Represents the estimated percentage ownership of the Company that will be held by Time Warner Cable stockholders. + References No definition available. + Details
Name: | cmcsa_AcquireeStockholdersPercentageOwnershipInParentCompany
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the amount of the Company's Class A common stock that Time Warner Cable stockholders will receive in exchange for each share of Time Warner Cable common stock owned immediately prior to the merger. + References No definition available. + Details
Name: | cmcsa_CompanySharesExchangedForEachAcquireeShare
Namespace Prefix: | cmcsa_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of customers + References No definition available. + Details
Name: | cmcsa_NumberOfCustomers
Namespace Prefix: | cmcsa_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The estimated ownership percentage in New Charter. + References No definition available. + Details
Name: | cmcsa_OwnershipPercentageInNewCharter
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The estimated ownership percentage in Spin Co. + References No definition available. + Details
Name: | cmcsa_OwnershipPercentageInSpinco
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | cmcsa_SignificantTransactionsLineItems
Namespace Prefix: | cmcsa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration