v3.5.0.2

Investments (Cost Method Investments) (Details) - Air Touch [Member] $ in Billions | Jun. 30, 2016 USD ($)
--- | ---
Fair value of AirTouch preferred stock related to redeemable preferred shares | $ 1.7
Fair value of redeemable preferred shares | $ 1.7

X
- Definition Fair value of our redeemable subsidiary preferred shares and/or stock + References No definition available. + Details
Name: | cmcsa_FairValueAmountOfRedeemablePreferredShares
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value of a cost method investment related to redeemable preferred shares. + References No definition available. + Details
Name: | cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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