v2.4.0.8

Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended |
--- | --- | ---
Sep. 30, 2014 | Dec. 31, 2013
Unrecognized tax benefits, interest on income taxes accrued | $ 460 | $ 780
Change In Income Tax Expense Related To Effectively Settled Uncertain Tax Positions | $ 724 |

X
- Definition Represents the change in income tax expense as a result of a reduction in the accrual for uncertain tax positions and related accrued interest on these tax positions, net of any indemnification. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant