v2.4.1.9

Share-Based Compensation (Recognized Share-Based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Recognized share-based compensation expense	$ 101us-gaap_AllocatedShareBasedCompensationExpense	$ 90us-gaap_AllocatedShareBasedCompensationExpense
NBCUniversal Media, LLC [Member]
Recognized share-based compensation expense	21us-gaap_AllocatedShareBasedCompensationExpense / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	18us-gaap_AllocatedShareBasedCompensationExpense / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Stock Options [Member]
Recognized share-based compensation expense	35us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember	36us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember
Stock Options [Member] | NBCUniversal Media, LLC [Member]
Recognized share-based compensation expense	2us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	3us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Restricted Share Units [Member]
Recognized share-based compensation expense	58us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember	48us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember
Restricted Share Units [Member] | NBCUniversal Media, LLC [Member]
Recognized share-based compensation expense	17us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	13us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_RestrictedStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Employee Stock Purchase Plan [Member]
Recognized share-based compensation expense	8us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember	6us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember
Employee Stock Purchase Plan [Member] | NBCUniversal Media, LLC [Member]
Recognized share-based compensation expense	$ 2us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	$ 2us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

+ Details

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Balance Type:	debit
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: