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: