v2.4.1.9

Significant Transactions (Narrative) (Details) (Transaction-Related Expenses Member, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Transaction-Related Expenses Member
Significant Transactions [Line Items]
Other operating and administrative expenses	$ 99cmcsa_Transactioncostsandtransactionrelatedcostsinoperatingcostsandexpenses / us-gaap_BusinessAcquisitionAxis = cmcsa_TransactionRelatedExpensesMember	$ 17cmcsa_Transactioncostsandtransactionrelatedcostsinoperatingcostsandexpenses / us-gaap_BusinessAcquisitionAxis = cmcsa_TransactionRelatedExpensesMember

X

- Details

Name:	cmcsa_SignificantTransactionsLineItems
Namespace Prefix:	cmcsa_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Transaction costs and transaction related costs in other operating costs and administrative expenses

+ References

No definition available.

+ Details

Name:	cmcsa_Transactioncostsandtransactionrelatedcostsinoperatingcostsandexpenses
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration