v2.4.1.9

Supplemental Financial Information (Receivables)(Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Receivables, gross	$ 6,634us-gaap_AccountsReceivableGrossCurrent	$ 6,885us-gaap_AccountsReceivableGrossCurrent
Less: Allowance for returns and customer incentives	297cmcsa_ReturnsAndIncentivesAllowance	359cmcsa_ReturnsAndIncentivesAllowance
Less: Allowance for doubtful accounts	193us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent	205us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Receivables, net	6,144us-gaap_AccountsReceivableNetCurrent	6,321us-gaap_AccountsReceivableNetCurrent
NBCUniversal Media, LLC [Member]
Receivables, gross	5,248us-gaap_AccountsReceivableGrossCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	5,258us-gaap_AccountsReceivableGrossCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Less: Allowance for returns and customer incentives	294cmcsa_ReturnsAndIncentivesAllowance / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	356cmcsa_ReturnsAndIncentivesAllowance / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Less: Allowance for doubtful accounts	63us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	60us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Receivables, net	$ 4,891us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	$ 4,842us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X

- Definition

A valuation allowance for sales returns and other incentives.

+ References

No definition available.

+ Details

Name:	cmcsa_ReturnsAndIncentivesAllowance
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 3

-Subparagraph a, b

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3-4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph a(1)

-Article 5



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: