Condensed Consolidating Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			$ 10,814	$ 9,794
Investing Activities
Net transactions with affiliates			0	0
Capital expenditures	$ (2,327)	$ (2,271)	(4,405)	(4,156)
Cash paid for intangible assets	(420)	(359)	(836)	(737)
Acquisitions and construction of real estate properties			(250)	(211)
Acquisitions, net of cash acquired			(398)	(126)
Proceeds from sales of investments			57	138
Purchases of investments			(1,825)	(580)
Other			170	(156)
Net cash provided by (used in) investing activities			(7,487)	(5,828)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			(1,695)	205
Proceeds from borrowings			8,963	4,753
Repurchases and repayments of debt			(4,967)	(2,551)
Repurchases of common stock under repurchase program and employee plans			(2,476)	(2,636)
Dividends paid			(1,404)	(1,281)
Purchase of Universal Studios Japan noncontrolling interests			(2,299)	0
Issuances of common stock			0	19
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			(137)	(125)
Other			80	20
Net cash provided by (used in) financing activities			(3,935)	(1,596)
Increase (decrease) in cash and cash equivalents			(608)	2,370
Cash and cash equivalents, beginning of period			3,301	2,295
Cash and cash equivalents, end of period	2,693	4,665	2,693	4,665
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
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
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	0	0
Comcast Parent [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net cash provided by operating activities			(465)	(367)
Investing Activities
Net transactions with affiliates			2,559	880
Capital expenditures			(3)	(7)
Cash paid for intangible assets			(2)	(3)
Acquisitions and construction of real estate properties			(143)	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			0	0
Purchases of investments			(20)	(15)
Other			101	(164)
Net cash provided by (used in) investing activities			2,492	691
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			(627)	(400)
Proceeds from borrowings			3,500	4,753
Repurchases and repayments of debt			(1,000)	(750)
Repurchases of common stock under repurchase program and employee plans			(2,476)	(2,636)
Dividends paid			(1,404)	(1,281)
Purchase of Universal Studios Japan noncontrolling interests			0
Issuances of common stock			0	19
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			0	0
Other			(20)	(29)
Net cash provided by (used in) financing activities			(2,027)	(324)
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	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			12,069	11,054
Investing Activities
Net transactions with affiliates			(3,728)	(2,543)
Capital expenditures			(4,402)	(4,149)
Cash paid for intangible assets			(834)	(734)
Acquisitions and construction of real estate properties			(107)	(211)
Acquisitions, net of cash acquired			(398)	(126)
Proceeds from sales of investments			47	36
Purchases of investments			(1,748)	(563)
Other			20	43
Net cash provided by (used in) investing activities			(11,150)	(8,247)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			(1,068)	605
Proceeds from borrowings			5,463	0
Repurchases and repayments of debt			(3,414)	(797)
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)
Issuances of common stock			0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			(137)	(125)
Other			100	24
Net cash provided by (used in) financing activities			(1,355)	(293)
Increase (decrease) in cash and cash equivalents			(436)	2,514
Cash and cash equivalents, beginning of period			2,819	1,881
Cash and cash equivalents, end of period	2,383	4,395	2,383	4,395
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			102	0
Investing Activities
Net transactions with affiliates			(102)	0
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			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			(102)	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
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	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			(116)	(84)
Investing Activities
Net transactions with affiliates			666	84
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			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			666	84
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			0	0
Proceeds from borrowings			0	0
Repurchases and repayments of debt			(550)	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
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			(550)	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	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			(776)	(809)
Investing Activities
Net transactions with affiliates			605	1,579
Capital expenditures			0	0
Cash paid for intangible assets			0	0
Acquisitions and construction of real estate properties			0	0
Acquisitions, net of cash acquired			0	0
Proceeds from sales of investments			10	102
Purchases of investments			(57)	(2)
Other			49	(35)
Net cash provided by (used in) investing activities			607	1,644
Financing Activities
Proceeds from (repayments of) short-term borrowings, net			0	0
Proceeds from borrowings			0	0
Repurchases and repayments of debt			(3)	(1,004)
Repurchases of common stock under repurchase program and employee plans			0	0
Dividends paid			0	0
Purchase of Universal Studios Japan noncontrolling interests			0
Issuances of common stock			0	0
Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock			0	0
Other			0	25
Net cash provided by (used in) financing activities			(3)	(979)
Increase (decrease) in cash and cash equivalents			(172)	(144)
Cash and cash equivalents, beginning of period			482	414
Cash and cash equivalents, end of period	$ 310	$ 270	$ 310	$ 270