Condensed Consolidating Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Operating Activities
Net cash provided by (used in) operating activities	$ 5,245	$ 4,486
Investing Activities
Net transactions with affiliates	0cmcsa_NetTransactionsWithAffiliates	0cmcsa_NetTransactionsWithAffiliates
Capital expenditures	(1,726)	(1,448)
Cash paid for intangible assets	(273)	(217)
Acquisitions and construction of real estate properties	(24)	0
Proceeds from sales of businesses and investments	180	300
Purchases of investments	(32)us-gaap_PaymentsToAcquireInvestments	(37)us-gaap_PaymentsToAcquireInvestments
Other	181	(103)
Net cash provided by (used in) investing activities	(1,694)	(1,505)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	(150)	(364)
Proceeds from borrowings	0us-gaap_ProceedsFromOtherDebt	2,187us-gaap_ProceedsFromOtherDebt
Repurchases and repayments of debt	(909)us-gaap_RepaymentsOfOtherDebt	(2,260)us-gaap_RepaymentsOfOtherDebt
Repurchases and retirements of common stock	(2,000)	(750)
Dividends paid	(572)us-gaap_PaymentsOfDividends	(508)us-gaap_PaymentsOfDividends
Issuances of common stock	28	20
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	(62)	(66)
Other	141	96
Net cash provided by (used in) financing activities	(3,524)	(1,645)
Increase (decrease) in cash and cash equivalents	27	1,336
Cash and cash equivalents, beginning of period	3,910	1,718
Cash and cash equivalents, end of period	3,937	3,054
Elimination and Consolidation Adjustments [Member]
Operating Activities
Net cash provided by (used in) operating activities	0	0
Investing Activities
Net transactions with affiliates	0	0
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	0	0
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Comcast Parent [Member]
Operating Activities
Net cash provided by (used in) operating activities	(294)	(96)
Investing Activities
Net transactions with affiliates	3,609	1,370
Capital expenditures	(6)	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	(10)
Other	0	0
Net cash provided by (used in) investing activities	3,603	1,360
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	(1,350)
Proceeds from borrowings	0	2,184
Repurchases and repayments of debt	(900)	(1,000)
Repurchases and retirements of common stock	(2,000)	(750)
Dividends paid	(572)	(508)
Issuances of common stock	28	20
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	135	140
Net cash provided by (used in) financing activities	(3,309)	(1,264)
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Comcast Holdings [Member]
Operating Activities
Net cash provided by (used in) operating activities	(1)	(2)
Investing Activities
Net transactions with affiliates	1	2
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	1	2
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
CCCL Parent [Member]
Operating Activities
Net cash provided by (used in) operating activities	82	110
Investing Activities
Net transactions with affiliates	(82)	(110)
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	(82)	(110)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Combined CCHMO Parents [Member]
Operating Activities
Net cash provided by (used in) operating activities	(48)	(47)
Investing Activities
Net transactions with affiliates	48	47
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	48	47
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
NBCUniversal Media Parent [Member]
Operating Activities
Net cash provided by (used in) operating activities	(361)	(306)
Investing Activities
Net transactions with affiliates	321	483
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions and construction of real estate properties	0	0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	(6)
Other	(5)	0
Net cash provided by (used in) investing activities	316	477
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	(1)	(1)
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	(1)	(1)
Increase (decrease) in cash and cash equivalents	(46)	170
Cash and cash equivalents, beginning of period	385	336
Cash and cash equivalents, end of period	339	506
Comcast Non-Guarantor Subsidiaries [Member]
Operating Activities
Net cash provided by (used in) operating activities	5,867	4,827
Investing Activities
Net transactions with affiliates	(3,897)	(1,792)
Capital expenditures	(1,720)	(1,448)
Cash paid for intangible assets	(273)	(217)
Acquisitions and construction of real estate properties	(24)	0
Proceeds from sales of businesses and investments	180	300
Purchases of investments	(32)	(21)
Other	186	(103)
Net cash provided by (used in) investing activities	(5,580)	(3,281)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	(150)	986
Proceeds from borrowings	0	3
Repurchases and repayments of debt	(8)	(1,259)
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	(62)	(66)
Other	6	(44)
Net cash provided by (used in) financing activities	(214)	(380)
Increase (decrease) in cash and cash equivalents	73	1,166
Cash and cash equivalents, beginning of period	3,525	1,382
Cash and cash equivalents, end of period	$ 3,598	$ 2,548

Decrease in noncontrolling interest balance from payment of dividends or other distributions by the non-wholly owned subsidiary or partially owned entity, included in the consolidation of the parent entity, to the noncontrolling interest holders and dividends for redeemable subsidiary preferred stock.

No definition available.