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]	Class B Common Stock [Member] Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effects of adoption of accounting standards	$ 33			$ (43)		$ 76		$ 0		$ (232)	$ 232
Beginning balance at Dec. 31, 2017	69,459		$ 37,497	38,202	$ (7,517)	379	$ 843						$ 55	$ 0
Beginning balance at Dec. 31, 2017								43,041		42,148	(20)	$ 913
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation plans	127		127
Repurchases of common stock under repurchase program and employee plans	(1,726)		(294)	(1,432)
Employee stock purchase plans	48		48
Dividends declared	(884)			(884)				(195)		(195)
Other comprehensive income (loss)	157					153	4	188			184	4
Contributions from (distributions to) noncontrolling interests, net	350						350	346				346
Other	(6)		(3)				(3)	(10)		(6)		(4)
Net income (loss)	3,152			3,118			34	1,540		1,513		27
Ending balance at Mar. 31, 2018	70,710		37,375	38,961	(7,517)	608	1,228						55	0
Ending balance at Mar. 31, 2018								44,910		43,228	396	1,286
Beginning balance at Dec. 31, 2017		$ 1,357							$ 409
Increase (Decrease) in Temporary Equity [Roll Forward]
Contributions from (distributions to) noncontrolling interests, net		(17)							(17)
Other		(10)
Net income (loss)		24							13
Ending balance at Mar. 31, 2018		1,354							405
Beginning balance at Dec. 31, 2018	72,502		37,461	41,983	(7,517)	(368)	889						54	0
Beginning balance at Dec. 31, 2018								46,781		45,618	254	909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation plans	174		174
Repurchases of common stock under repurchase program and employee plans	(255)		(62)	(193)
Employee stock purchase plans	48		48
Dividends declared	(964)			(964)				(238)		(238)
Other comprehensive income (loss)	800					790	10	(22)			(32)	10
Contributions from (distributions to) noncontrolling interests, net	(46)						(46)	(46)				(46)
Other	(1)						(1)	(3)				(3)
Net income (loss)	3,604			3,553			51	1,822		1,784		38
Ending balance at Mar. 31, 2019	75,862		$ 37,621	$ 44,379	$ (7,517)	$ 422	$ 903						$ 54	$ 0
Ending balance at Mar. 31, 2019								48,294		$ 47,164	$ 222	$ 908
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		(20)							(23)
Other		(8)
Net income (loss)		28							16
Ending balance at Mar. 31, 2019	$ 1,316	$ 1,316						$ 382	$ 382