Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Redeemable Noncontrolling Interests And Redeemable Subsidiary Preferred Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock at Cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]	NBCUniversal Media LLC [Member]	NBCUniversal Media LLC [Member] Member's Capital [Member]	NBCUniversal Media LLC [Member] Accumulated Other Comprehensive Income (Loss) [Member]	NBCUniversal Media LLC [Member] Noncontrolling Interests [Member]	NBCUniversal Media LLC [Member] Redeemable Noncontrolling Interest [Member]	Class A Common Stock [Member] Common Stock [Member]	Class B Common Stock [Member] Common Stock [Member]
Beginning balance at Dec. 31, 2016		$ 1,446										$ 530
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(39)										(65)
Other		(123)										(84)
Net income (loss)		73										28
Ending balance at Dec. 31, 2017		1,357										409
Beginning balance at Dec. 31, 2016			$ 38,230	$ 23,065		$ 98	$ 2,231						$ 56	$ 0
Beginning balance at Dec. 31, 2016									$ 38,894	$ (135)	$ 2,116
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation plans			554
Repurchases of common stock under repurchase program and employee plans			(832)	(4,623)									(1)
Employee stock purchase plans			190
Dividends declared				(2,975)
Distributions to member									(1,968)
Other comprehensive income (loss)						87	81			(26)	81
Contributions from (distributions to) noncontrolling interests, net							(108)				(120)
Contributions from member									662
Purchase of Universal Studios Japan noncontrolling interests			(696)			194	(1,736)		(704)	141	(1,736)
Other			51				261		184		466
Net Income Attributable to Comcast Corporation	$ 22,735			22,735				$ 5,080	5,080
Net income (loss)							114	134			106
Ending balance at Dec. 31, 2017	$ 69,459		37,497	38,202	$ (7,517)	379	843						55	0
Ending balance at Dec. 31, 2017								43,041	42,148	(20)	913
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.63
Contributions from (distributions to) noncontrolling interests, net		(56)										(52)
Other		(43)										(4)
Net income (loss)		58										36
Ending balance at Dec. 31, 2018	$ 1,316	1,316						389				389
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation plans			607
Repurchases of common stock under repurchase program and employee plans			(920)	(4,408)									(1)
Employee stock purchase plans			214
Dividends declared				(3,499)
Distributions to member									(1,627)
Other comprehensive income (loss)						(823)	(41)			42	(41)
Contributions from (distributions to) noncontrolling interests, net							294				299
Contributions from member									0
Purchase of Universal Studios Japan noncontrolling interests			0			0	0		0	0	0
Other			63				(280)		92		(294)
Net Income Attributable to Comcast Corporation	11,731			11,731				5,237	5,237
Net income (loss)							73	68			32
Ending balance at Dec. 31, 2018	$ 72,502		37,461	41,983	(7,517)	(368)	889						54	0
Ending balance at Dec. 31, 2018								46,781	45,618	254	909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.76
Contributions from (distributions to) noncontrolling interests, net		(62)										(59)
Other		(38)										4
Net income (loss)		156										118
Ending balance at Dec. 31, 2019	$ 1,372	$ 1,372						452				$ 452
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation plans			783
Repurchases of common stock under repurchase program and employee plans			(34)	(485)									0
Employee stock purchase plans			222
Dividends declared				(3,860)
Distributions to member									(2,362)
Other comprehensive income (loss)						1,415	(13)			(40)	(12)
Contributions from (distributions to) noncontrolling interests, net							176				189
Contributions from member									0
Purchase of Universal Studios Japan noncontrolling interests			0			0	0		0	0	0
Other			15				(14)		0		(16)
Net Income Attributable to Comcast Corporation	13,057			13,057				5,784	5,784
Net income (loss)							110	180			62
Ending balance at Dec. 31, 2019	$ 83,874		$ 38,447	$ 50,695	$ (7,517)	$ 1,047	$ 1,148						$ 54	$ 0
Ending balance at Dec. 31, 2019								$ 50,386	$ 49,040	$ 214	$ 1,132
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.84