v2.4.1.9

Supplemental Financial Information (Noncash Investing and Financing Activities)(Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015
Dividends payable, amount | $ 630 us-gaap_DividendsPayableCurrentAndNoncurrent
Dividends payable, amount per share | $ 0.25 us-gaap_DividendsPayableAmountPerShare
Capital expenditures incurred but not yet paid | 978 us-gaap_CapitalExpendituresIncurredButNotYetPaid
Fair Value Equity Securities Settlement | 517 cmcsa_FairValueEquitySecuritiesSettlement
Capital contribution accrued but not yet paid | 123 cmcsa_CapitalContributionAccruedButNotYetPaid
NBCUniversal Media, LLC [Member] |
Capital expenditures incurred but not yet paid | 153 us-gaap_CapitalExpendituresIncurredButNotYetPaid / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember
Capital contribution accrued but not yet paid | $ 123 cmcsa_CapitalContributionAccruedButNotYetPaid / cmcsa_LegalEntity1Axis = cmcsa_NBCUniversalMediaLLCMember

X
- Definition The carrying value of a liability for a capital contribution for an investment that was accrued but not yet paid + References No definition available. + Details
Name: | cmcsa_CapitalContributionAccruedButNotYetPaid
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value method equity securities used to settle our obligations under prepaid forward sale agreements in the period. + References No definition available. + Details
Name: | cmcsa_FairValueEquitySecuritiesSettlement
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
Name: | us-gaap_CapitalExpendituresIncurredButNotYetPaid
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The per share amount of a dividend declared, but not paid, as of the financial reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
Name: | us-gaap_DividendsPayableAmountPerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph a -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph 5 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_DividendsPayableCurrentAndNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | cmcsa_LegalEntity1Axis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |