Condensed 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 Interest [Member]	NBCUniversal Media LLC [Member]	NBCUniversal Media LLC [Member] Redeemable Noncontrolling Interest [Member]	NBCUniversal Media LLC [Member] Member's Capital [Member]	NBCUniversal Media LLC [Member] Accumulated Other Comprehensive Income (Loss) [Member]	NBCUniversal Media LLC [Member] Noncontrolling Interest [Member]	Class A Common Stock [Member] Common Stock [Member]
Beginning balance at Dec. 31, 2017		$ 1,357							$ 409
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(42)							(43)
Other		(35)							(5)
Net income (loss)		37							26
Ending balance at Sep. 30, 2018		1,317							387
Beginning balance at Dec. 31, 2017			$ 37,497	$ 38,202	$ (7,517)	$ 379	$ 843						$ 55
Beginning balance at Dec. 31, 2017										$ 42,148	$ (20)	$ 913
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distributions to member										(1,228)
Stock compensation plans			434
Repurchases of common stock under repurchase program and employee plans			(757)	(3,530)									(1)
Employee stock purchase plans			161
Dividends declared				(2,631)
Other comprehensive income (loss)						(81)	(45)				(114)	(45)
Contributions from (distributions to) noncontrolling interests, net							277					272
Other			59	0			(276)			92		(293)
Net income (loss)				9,220			23			3,991		(4)
Ending balance at Sep. 30, 2018	$ 72,345		37,394	41,218	(7,517)	374	822						54
Ending balance at Sep. 30, 2018								$ 45,712		44,771	98	843
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.57
Beginning balance at Jun. 30, 2018		1,343							391
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(11)							(10)
Other		(11)							0
Net income (loss)		(4)							6
Ending balance at Sep. 30, 2018		1,317							387
Beginning balance at Jun. 30, 2018			37,427	40,269	(7,517)	461	1,049						54
Beginning balance at Jun. 30, 2018										43,777	218	1,090
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distributions to member										(238)
Stock compensation plans			144
Repurchases of common stock under repurchase program and employee plans			(228)	(1,064)									0
Employee stock purchase plans			49
Dividends declared				(871)
Other comprehensive income (loss)						(87)	(20)				(120)	(20)
Contributions from (distributions to) noncontrolling interests, net							(40)					(41)
Other			2	(2)			(181)			1		(191)
Net income (loss)				2,886			14			1,231		5
Ending balance at Sep. 30, 2018	$ 72,345		37,394	41,218	(7,517)	374	822						54
Ending balance at Sep. 30, 2018								45,712		44,771	98	843
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.19
Beginning balance at Dec. 31, 2018	$ 1,316	1,316						389	389
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(49)							(51)
Other		(28)							3
Net income (loss)		129							101
Ending balance at Sep. 30, 2019	1,368	1,368						442	442
Beginning balance at Dec. 31, 2018	72,502		37,461	41,983	(7,517)	(368)	889						54
Beginning balance at Dec. 31, 2018								46,781		45,618	254	909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distributions to member										(2,020)
Stock compensation plans			604
Repurchases of common stock under repurchase program and employee plans			(39)	(406)									0
Employee stock purchase plans			166
Dividends declared				(2,893)
Other comprehensive income (loss)						(791)	(24)				29	(25)
Contributions from (distributions to) noncontrolling interests, net							66					76
Other			4	(9)			(14)			0		(12)
Net income (loss)				9,895			99			4,611		65
Ending balance at Sep. 30, 2019	$ 79,160		38,196	48,570	(7,517)	(1,159)	1,016						54
Ending balance at Sep. 30, 2019								49,505		48,209	283	1,013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.63
Beginning balance at Jun. 30, 2019		1,329							401
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(12)							(13)
Other		(9)							3
Net income (loss)		60							51
Ending balance at Sep. 30, 2019	$ 1,368	$ 1,368						442	$ 442
Beginning balance at Jun. 30, 2019			37,950	46,425	(7,517)	(62)	980						54
Beginning balance at Jun. 30, 2019										47,529	295	988
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distributions to member										(576)
Stock compensation plans			193
Repurchases of common stock under repurchase program and employee plans			6	(101)									0
Employee stock purchase plans			51
Dividends declared				(965)
Other comprehensive income (loss)						(1,097)	(22)				(12)	(23)
Contributions from (distributions to) noncontrolling interests, net							50					51
Other			(4)	(6)			(3)			0		(6)
Net income (loss)				3,217			11			1,256		3
Ending balance at Sep. 30, 2019	$ 79,160		$ 38,196	$ 48,570	$ (7,517)	$ (1,159)	$ 1,016						$ 54
Ending balance at Sep. 30, 2019								$ 49,505		$ 48,209	$ 283	$ 1,013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared per common share (in dollars per share)	$ 0.21