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Condensed Consolidating Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			$ 12,537	$ 10,749
Investing Activities
Net transactions with affiliates			0	0
Capital expenditures	$ (2,250)	$ (2,327)	(4,223)	(4,405)
Cash paid for intangible assets	(511)	(386)	(930)	(771)
Acquisitions and construction of real estate properties			(104)	(250)
Construction of Universal Beijing Resort			(116)	(29)
Acquisitions, net of cash acquired			(88)	(398)
Proceeds from sales of investments			113	57
Purchases of investments			(538)	(1,825)
Other			580	214
Net cash provided by (used in) investing activities			(5,306)	(7,407)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			23	(1,695)
Proceeds from borrowings			4,279	8,963
Repurchases and repayments of debt			(4,347)	(4,967)
Repurchases of common stock under repurchase program and employee plans			(2,998)	(2,476)
Dividends paid			(1,616)	(1,404)
Purchase of Universal Studios Japan noncontrolling interests			0	(2,299)
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			(140)	(137)
Other			(161)	80
Net cash provided by (used in) financing activities			(4,960)	(3,935)
Increase (decrease) in cash, cash equivalents and restricted cash			2,271	(593)
Cash, cash equivalents and restricted cash, beginning of period			3,571	3,415
Cash, cash equivalents and restricted cash, end of period	5,842	2,822	5,842	2,822
Elimination and Consolidation Adjustments [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by 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
Construction of Universal Beijing Resort			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of 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 of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests				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, cash equivalents and restricted cash			0	0
Cash, cash equivalents and restricted cash, beginning of period			0	0
Cash, cash equivalents and restricted cash, end of period	0	0	0	0
Comcast Parent [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			(491)	(465)
Investing Activities
Net transactions with affiliates			4,096	2,559
Capital expenditures			(10)	(3)
Cash paid for intangible assets			(2)	(2)
Acquisitions and construction of real estate properties			(76)	(143)
Construction of Universal Beijing Resort			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			0	0
Purchases of investments			(28)	(20)
Other			0	101
Net cash provided by (used in) investing activities			3,980	2,492
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			(902)	(627)
Proceeds from borrowings			3,973	3,500
Repurchases and repayments of debt			(1,900)	(1,000)
Repurchases of common stock under repurchase program and employee plans			(2,998)	(2,476)
Dividends paid			(1,616)	(1,404)
Purchase of Universal Studios Japan noncontrolling interests				0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			0	0
Other			(46)	(20)
Net cash provided by (used in) financing activities			(3,489)	(2,027)
Increase (decrease) in cash, cash equivalents and restricted cash			0	0
Cash, cash equivalents and restricted cash, beginning of period			0	0
Cash, cash equivalents and restricted cash, end of period	0	0	0	0
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			13,896	12,004
Investing Activities
Net transactions with affiliates			(4,290)	(3,728)
Capital expenditures			(4,213)	(4,402)
Cash paid for intangible assets			(928)	(769)
Acquisitions and construction of real estate properties			(28)	(107)
Construction of Universal Beijing Resort			(116)	(29)
Acquisitions, net of cash acquired			(88)	(398)
Proceeds from sales of investments			46	47
Purchases of investments			(480)	(1,748)
Other			131	64
Net cash provided by (used in) investing activities			(9,966)	(11,070)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			925	(1,068)
Proceeds from borrowings			306	5,463
Repurchases and repayments of debt			(2,444)	(3,414)
Repurchases of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests				(2,299)
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			(140)	(137)
Other			(115)	100
Net cash provided by (used in) financing activities			(1,468)	(1,355)
Increase (decrease) in cash, cash equivalents and restricted cash			2,462	(421)
Cash, cash equivalents and restricted cash, beginning of period			3,075	2,933
Cash, cash equivalents and restricted cash, end of period	5,537	2,512	5,537	2,512
Comcast Holdings [Member] | Subsidiary Issuer [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			6	102
Investing Activities
Net transactions with affiliates			(455)	(102)
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			0	0
Construction of Universal Beijing Resort			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			0	0
Purchases of investments			0	0
Other			449	0
Net cash provided by (used in) investing activities			(6)	(102)
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 of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests				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, cash equivalents and restricted cash			0	0
Cash, cash equivalents and restricted cash, beginning of period			0	0
Cash, cash equivalents and restricted cash, end of period	0	0	0	0
CCCL Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			(78)	(116)
Investing Activities
Net transactions with affiliates			78	666
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			0	0
Construction of Universal Beijing Resort			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			0	0
Purchases of investments			0	0
Other			0	0
Net cash provided by (used in) investing activities			78	666
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			0	0
Proceeds from borrowings			0	0
Repurchases and repayments of debt			0	(550)
Repurchases of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests				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	(550)
Increase (decrease) in cash, cash equivalents and restricted cash			0	0
Cash, cash equivalents and restricted cash, beginning of period			0	0
Cash, cash equivalents and restricted cash, end of period	0	0	0	0
NBCUniversal Media Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			(796)	(776)
Investing Activities
Net transactions with affiliates			571	605
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			0	0
Construction of Universal Beijing Resort			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			67	10
Purchases of investments			(30)	(57)
Other			0	49
Net cash provided by (used in) investing activities			608	607
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			0	0
Proceeds from borrowings			0	0
Repurchases and repayments of debt			(3)	(3)
Repurchases of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests				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			(3)	(3)
Increase (decrease) in cash, cash equivalents and restricted cash			(191)	(172)
Cash, cash equivalents and restricted cash, beginning of period			496	482
Cash, cash equivalents and restricted cash, end of period	$ 305	$ 310	$ 305	$ 310

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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