v2.4.0.6

Fair Value Disclosure Rollforward (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Discount rate used to determine fair value, minimum	5.60%
Discount rate used to determine fair value, maximum	13.00%
Contractual Obligations [Member]
Balance	$ 1,004
Acquisition accounting adjustments	(20)
Fair value adjustments	41
Payments	(41)
Balance	984
Contingent Consideration [Member]
Balance	583
Acquisition accounting adjustments	0
Fair value adjustments	41
Payments	(26)
Balance	$ 598

X

- Definition

This element represents the maximum range of the discount rate used to determine the fair value of, but not limited to, contractual obligations and contingent considerations.

+ References

No definition available.

+ Details

Name:	cmcsa_DiscountRateUsedToDetermineFairValueMaximum
Namespace Prefix:	cmcsa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This element represents the minimum range of the discount rate used to determine the fair value of, but not limited to, contractual obligations and contingent considerations.

+ References

No definition available.

+ Details

Name:	cmcsa_DiscountRateUsedToDetermineFairValueMinimum
Namespace Prefix:	cmcsa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This element represents the acquisition accounting adjustments recorded during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisAcquisitionAccountingAdjustments
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This element represents other fair value adjustments recorded during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisFairValueAdjustment
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

X

- Definition

This element represents the payments made during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

Name:	cmcsa_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisPayments
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This element represents a liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant