v2.4.1.9

Long-Term Debt (Debt Borrowings) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014
Senior 3.60% Notes Due 2024 [Member] |
Principal amount | $ 1,200 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = cmcsa_Senior360NotesDue2024Member
Interest rate | 3.60%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cmcsa_Senior360NotesDue2024Member
Maturity date | 2024
Senior 4.75% Notes Due 2044 [Member] |
Principal amount | 1,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = cmcsa_Senior475NotesDue2044Member
Interest rate | 4.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cmcsa_Senior475NotesDue2044Member
Maturity date | 2044
Senior 4.200% Notes Due 2034 [Member] |
Principal amount | 1,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = cmcsa_Senior4200NotesDue2034Member
Interest rate | 4.20%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cmcsa_Senior4200NotesDue2034Member
Maturity date | 2034
Senior 3.375% Notes Due 2025 [Member] |
Principal amount | 1,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = cmcsa_Senior3375NotesDue2025Member
Interest rate | 3.375%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cmcsa_Senior3375NotesDue2025Member
Maturity date | 2025
Current Year Borrowings [Member] |
Principal amount | $ 4,200 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = cmcsa_CurrentYearBorrowingsMember

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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_CurrentYearBorrowingsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_Senior3375NotesDue2025Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_Senior360NotesDue2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_Senior4200NotesDue2034Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=cmcsa_Senior475NotesDue2044Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |