Contributions from and (distributions to) noncontrolling interests.

No definition available.

Name:	cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Profit or loss as represented on the statement of changes in equity.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents an increase in non-controlling interest from issuance of additional equity interests to non-controlling interest holders or the sale of a portion of the parent's controlling interest and the impact on additional paid in capital.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of ownership interest in a limited liability company (LLC), including portions attributable to both the parent and noncontrolling interests.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

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-Publisher FASB

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-Topic 272

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669619-108580

+ Details

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Period Type:	duration

- Definition

Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4568447-111683

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-Topic 810

-SubTopic 10

-Section 55

-Paragraph 4I

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+ Details

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Period Type:	instant

- Definition

This element represents movements included in the statement of changes in stockholders' equity which are not separately disclosed or provided for elsewhere in the taxonomy.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Topic 505

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

+ Details

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- Definition

Value of stock (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of stock value of such awards forfeited. Stock issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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-Subparagraph (d)(1)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

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- Definition

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

+ References

+ Details

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Condensed Consolidated Statement of Changes in Equity (USD $) In Millions	Total	NBCUniversal Media, LLC [Member]	Redeemable Noncontrolling Interests And Redeemable Subisdiary Preferred Stock [Member]	Class A Common Stock [Member]	Class A Special Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock at Cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] NBCUniversal Media, LLC [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member] NBCUniversal Media, LLC [Member]	Redeemable Noncontrolling Interest [Member] NBCUniversal Media, LLC [Member]	Member's Capital [Member] NBCUniversal Media, LLC [Member]
Beginning balance at Dec. 31, 2013		$ 29,327									$ (16)		$ 287	$ 231	$ 29,056
Beginning Balance at Dec. 31, 2013	51,058		957	25	5	0	38,890	19,235	(7,517)	56		364
Stock compensation plans	36						242	(206)
Repurchases and retirements of common stock	(750)						(172)	(578)
Employee stock purchase plans	26						26
Other comprehensive income (loss)	(23)	3								(23)	3
Dividends declared	(585)us-gaap_DividendsCommonStockCash	(195)						(585)							(195)
Issuance of subsidiary shares to noncontrolling interests			82											82
Contributions from (distributions to) noncontrolling interests, net	(37)	(44)	(5)									(37)	(44)	(10)
Other	(7)us-gaap_StockholdersEquityOther		(5)				(1)					(6)	1		(1)
Net income (loss)	1,914cmcsa_EquityProfitLoss	727	24					1,871				43	45	14	682
Ending Balance at Mar. 31, 2014	51,632	29,818	1,053	25	5	0	38,985	19,737	(7,517)	33	(13)	364	289	317	29,542
Beginning balance at Dec. 31, 2014		30,637									(159)		267	330	30,529
Beginning Balance at Dec. 31, 2014	53,068		1,066	25	5	0	38,805	21,539	(7,517)	(146)		357
Stock compensation plans	43						232	(189)
Repurchases and retirements of common stock	(2,000)						(407)	(1,593)
Employee stock purchase plans	30						30
Other comprehensive income (loss)	(42)	(51)								(42)	(51)
Dividends declared	(630)us-gaap_DividendsCommonStockCash	(195)						(630)							(195)
Contributions from (distributions to) noncontrolling interests, net	(34)	(41)										(34)	(41)	(10)
Other	(39)us-gaap_StockholdersEquityOther	(15)	7									(39)	(14)		(1)
Net income (loss)	2,115cmcsa_EquityProfitLoss	902	26					2,059				56	50	16	852
Ending Balance at Mar. 31, 2015	52,511		1,099	25	5	0	38,660	21,186	(7,517)	(188)		340
Ending balance at Mar. 31, 2015		$ 31,237									$ (210)		$ 262	$ 336	$ 31,185