v3.7.0.1

Investments (Tables) | 3 Months Ended
--- | ---
Mar. 31, 2017
Fair Value, Equity And Cost Method Investments [Line Items] |
Investment Summary |
(in millions) | March 31, 2017 | December 31, 2016
Fair Value Method: |  |
Snap | $ | 662 |  | $ | — |
Other | 161 |  | 198 |
| 823 |  | 198 |
Equity Method: |  |  |  |
Atairos | 1,624 |  | 1,601 |
Hulu | 171 |  | 225 |
Other | 631 |  | 550 |
| 2,426 |  | 2,376 |
Cost Method: |  |
AirTouch | 1,602 |  | 1,599 |
BuzzFeed | 400 |  | 400 |
Other | 698 |  | 771 |
| 2,700 |  | 2,770 |
Total investments | 5,949 |  | 5,344 |
Less: Current investments | 11 |  | 97 |
Noncurrent investments | $ | 5,938 |  | $ | 5,247 |
Investment Income (Loss), Net | Investment Income (Loss), Net
| Three Months Ended March 31
(in millions) | 2017 | 2016
Gains (losses) on sales and exchanges of investments, net | $ | (1 | ) | $ | 2 |
Investment impairment losses | (4 | ) | (20 | )
Interest and dividend income | 33 |  | 29 |
Other, net | 31 |  | 19 |
Investment income (loss), net | $ | 59 |  | $ | 30 |
NBCUniversal Media LLC [Member] |
Fair Value, Equity And Cost Method Investments [Line Items] |
Investment Summary |
(in millions) | March 31, 2017 | December 31, 2016
Fair Value Method: |  |  |  |
Snap | $ | 662 |  | $ | — |
Other | 7 |  | 6 |
| 669 |  | 6 |
Equity Method: |  |  |  |
Hulu | 171 |  | 225 |
Other | 400 |  | 336 |
| 571 |  | 561 |
Cost Method: |  |  |  |
BuzzFeed | 400 |  | 400 |
Other | 300 |  | 296 |
| 700 |  | 696 |
Total investments | $ | 1,940 |  | $ | 1,263 |

X
- Definition Tabular disclosure of investment income (loss), including, but not limited to gains on sales and exchanges of investments, other than temporary impairment losses and interest and dividend income. + References No definition available. + Details
Name: | cmcsa_ComponentsOfInvestmentIncomeLossNetTableTextBlock
Namespace Prefix: | cmcsa_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition [Line Items] for Fair Value, Equity And Cost Method Investments [Table] + References No definition available. + Details
Name: | cmcsa_FairValueEquityAndCostMethodInvestmentsLineItems
Namespace Prefix: | cmcsa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the summary of investment holdings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010 + Details
Name: | us-gaap_SummaryInvestmentHoldingsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

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