v2.4.1.9

Investments (Fair Value Method Investments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Prepaid forward sale liabilities carrying value	$ 0cmcsa_LiabilitiesRelatedToPrepaidForwardSaleAgreements
Fair Value Equity Securities Settlement	$ 517cmcsa_FairValueEquitySecuritiesSettlement

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

The carrying value of the liabilities related to prepaid forward sale agreements.

+ References

No definition available.

+ Details

Name:	cmcsa_LiabilitiesRelatedToPrepaidForwardSaleAgreements
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant