Consolidated Statement of Cash Flows (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income	$ 8,592,000,000us-gaap_ProfitLoss	$ 7,135,000,000us-gaap_ProfitLoss	$ 7,865,000,000us-gaap_ProfitLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	8,019,000,000us-gaap_DepreciationAndAmortization	7,871,000,000us-gaap_DepreciationAndAmortization	7,798,000,000us-gaap_DepreciationAndAmortization
Share-based compensation	513,000,000us-gaap_ShareBasedCompensation	419,000,000us-gaap_ShareBasedCompensation	371,000,000us-gaap_ShareBasedCompensation
Noncash interest expense (income), net	180,000,000cmcsa_NoncashInterestExpenseIncomeNet	167,000,000cmcsa_NoncashInterestExpenseIncomeNet	193,000,000cmcsa_NoncashInterestExpenseIncomeNet
Equity in net (income) losses of investees, net	(97,000,000)	86,000,000	(959,000,000)
Cash received from investees	104,000,000	120,000,000	195,000,000
Net (gain) loss on investment activity and other	4,000,000	(169,000,000)	(1,062,000,000)
Deferred income taxes	1,165,000,000us-gaap_DeferredIncomeTaxExpenseBenefit	16,000,000us-gaap_DeferredIncomeTaxExpenseBenefit	139,000,000us-gaap_DeferredIncomeTaxExpenseBenefit
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Current and noncurrent receivables, net	(33,000,000)	(721,000,000)	(823,000,000)
Film and television costs, net	(562,000,000)cmcsa_FilmAndTelevisionCostsNet	44,000,000cmcsa_FilmAndTelevisionCostsNet	22,000,000cmcsa_FilmAndTelevisionCostsNet
Accounts payable and accrued expenses related to trade creditors	153,000,000	(667,000,000)	366,000,000
Other operating assets and liabilities	(1,093,000,000)	(141,000,000)	749,000,000
Net cash provided by operating activities	16,945,000,000	14,160,000,000	14,854,000,000
Investing Activities
Capital expenditures	(7,420,000,000)	(6,596,000,000)	(5,714,000,000)
Cash paid for intangible assets	(1,122,000,000)	(1,009,000,000)	(923,000,000)
Acquisitions and construction of real estate properties	(43,000,000)	(1,904,000,000)	0
Acquisitions, net of cash acquired	(477,000,000)	(99,000,000)	(90,000,000)
Proceeds from sales of businesses and investments	666,000,000	1,083,000,000	3,102,000,000
Return of capital from investees	25,000,000	149,000,000	2,362,000,000
Purchases of investments	(191,000,000)us-gaap_PaymentsToAcquireInvestments	(1,223,000,000)us-gaap_PaymentsToAcquireInvestments	(297,000,000)us-gaap_PaymentsToAcquireInvestments
Other	(171,000,000)	85,000,000	74,000,000
Net cash provided by (used in) investing activities	(8,733,000,000)	(9,514,000,000)	(1,486,000,000)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	(504,000,000)	1,345,000,000	(544,000,000)
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Repurchases and repayments of debt	(3,175,000,000)us-gaap_RepaymentsOfOtherDebt	(2,444,000,000)us-gaap_RepaymentsOfOtherDebt	(2,881,000,000)us-gaap_RepaymentsOfOtherDebt
Repurchases and retirements of common stock	(4,251,000,000)	(2,000,000,000)	(3,000,000,000)
Dividends paid	(2,254,000,000)us-gaap_PaymentsOfDividends	(1,964,000,000)us-gaap_PaymentsOfDividends	(1,608,000,000)us-gaap_PaymentsOfDividends
Issuances of common stock	35,000,000	40,000,000	233,000,000
Purchase of NBCUniversal noncontrolling common equity interest	0	(10,761,000,000)	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock	(220,000,000)	(215,000,000)	(691,000,000)
Settlement of Station Venture liability	0	(602,000,000)	0
Other	167,000,000	(211,000,000)	(90,000,000)
Net cash provided by (used in) financing activities	(6,020,000,000)	(13,879,000,000)	(4,037,000,000)
Increase (decrease) in cash and cash equivalents	2,192,000,000	(9,233,000,000)	9,331,000,000
Cash and cash equivalents, beginning of year	1,718,000,000	10,951,000,000	1,620,000,000
Cash and cash equivalents, end of year	3,910,000,000	1,718,000,000	10,951,000,000
NBCUniversal Media, LLC [Member]
Operating Activities
Net income	3,297,000,000	2,122,000,000	3,231,000,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,495,000,000	1,411,000,000	1,326,000,000
Share-based compensation	0	7,000,000	7,000,000
Equity in net (income) losses of investees, net	(46,000,000)	93,000,000	(183,000,000)
Cash received from investees	74,000,000	90,000,000	189,000,000
Net (gain) loss on investment activity and other	136,000,000	345,000,000	(1,093,000,000)
Deferred income taxes	(12,000,000)	(10,000,000)	15,000,000
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Current and noncurrent receivables, net	(25,000,000)	(752,000,000)	(643,000,000)
Film and television costs, net	(571,000,000)	2,000,000	100,000,000
Accounts payable and accrued expenses related to trade creditors	(88,000,000)	(789,000,000)	51,000,000
Other operating assets and liabilities	264,000,000	505,000,000	333,000,000
Net cash provided by operating activities	4,524,000,000	3,024,000,000	3,333,000,000
Investing Activities
Capital expenditures	(1,221,000,000)	(1,160,000,000)	(763,000,000)
Cash paid for intangible assets	(130,000,000)	(113,000,000)	(113,000,000)
Acquisitions of real estate properties	0	(1,705,000,000)	0
Acquisitions, net of cash acquired	(118,000,000)	(111,000,000)	(90,000,000)
Proceeds from sales of businesses and investments	13,000,000	2,000,000	3,026,000,000
Return of capital from investees	24,000,000	131,000,000	75,000,000
Purchases of investments	(35,000,000)	(236,000,000)	(117,000,000)
Other	(146,000,000)	(20,000,000)	(9,000,000)
Net cash provided by (used in) investing activities	(1,613,000,000)	(3,212,000,000)	2,009,000,000
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0	(550,000,000)
Proceeds from borrowings	0	0	1,995,000,000
Repurchases and repayments of debt	(906,000,000)	(92,000,000)	(413,000,000)
Proceeds from (repayments of) borrowings from Comcast, net	97,000,000	799,000,000	0
Redemption transaction distribution	0	(3,200,000,000)	0
Distributions to member	(1,641,000,000)	(1,422,000,000)	(964,000,000)
Distributions to noncontrolling interests	(177,000,000)	(183,000,000)	(216,000,000)
Settlement of Station Venture liability	0	(602,000,000)	0
Other	(3,000,000)	(66,000,000)	(81,000,000)
Net cash provided by (used in) financing activities	(2,630,000,000)	(4,766,000,000)	(229,000,000)
Increase (decrease) in cash and cash equivalents	281,000,000	(4,954,000,000)	5,113,000,000
Cash and cash equivalents, beginning of year	967,000,000	5,921,000,000	808,000,000
Cash and cash equivalents, end of year	$ 1,248,000,000	$ 967,000,000	$ 5,921,000,000

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-Section 45

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The cash outflow to reacquire common stock during the period.

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Cash outflow to owners or shareholders, excluding ordinary dividends. Includes special dividends.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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The cash outflow associated with the purchase of noncontrolling interest during the period.

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The cash outflow for acquisition of buildings (properties) whether for investment or use.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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The cash outflow to acquire asset without physical form usually arising from contractual or other legal rights, excluding goodwill.

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The cash outflow associated with the purchase of all investments (debt, security, other) during the period.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Cash dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations that are returns of capital. Excludes dividends or distributions from equity method investments classified as operating activities.

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No definition available.

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The cash inflow from the additional capital contribution to the entity.

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The cash inflow from other borrowing not otherwise defined in the taxonomy.

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The net cash inflow or outflow from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy.

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The net cash inflow or outflow for borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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The cash outflow for the payment of other borrowing not otherwise defined in the taxonomy.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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