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Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 21,735	$ 21,286	$ 44,526	$ 41,873
Cable Communications [Member]
Disaggregation of Revenue [Line Items]
Revenue	13,710	13,257	27,228	26,307
Cable Communications [Member] | Residential, Video [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,628	5,740	11,287	11,446
Cable Communications [Member] | Residential, High-Speed Internet [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,262	3,898	8,419	7,740
Cable Communications [Member] | Residential, Voice [Member]
Disaggregation of Revenue [Line Items]
Revenue	994	1,034	2,000	2,068
Cable Communications [Member] | Business Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,761	1,585	3,487	3,128
Cable Communications [Member] | Advertising [Member]
Disaggregation of Revenue [Line Items]
Revenue	666	626	1,248	1,180
Cable Communications [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 399	$ 374	$ 787	$ 745
Cable Communications [Member] | Franchise And Other Regulatory Fees [Member]
Disaggregation of Revenue [Line Items]
Cable segment revenue types as percentage of total cable revenue	2.70%	2.80%	2.70%	2.80%
Cable Networks [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 2,916	$ 2,696	$ 6,110	$ 5,336
Cable Networks [Member] | Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,684	1,550	3,571	3,112
Cable Networks [Member] | Advertising [Member]
Disaggregation of Revenue [Line Items]
Revenue	938	906	1,926	1,732
Cable Networks [Member] | Content Licensing And Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	294	240	613	492
Broadcast Television [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,391	2,241	5,888	4,449
Broadcast Television [Member] | Advertising [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,387	1,270	3,752	2,549
Broadcast Television [Member] | Content Licensing [Member]
Disaggregation of Revenue [Line Items]
Revenue	481	523	1,003	1,026
Broadcast Television [Member] | Distribution And Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	523	448	1,133	874
Filmed Entertainment [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,710	2,142	3,357	4,109
Filmed Entertainment [Member] | Theatrical [Member]
Disaggregation of Revenue [Line Items]
Revenue	540	837	963	1,488
Filmed Entertainment [Member] | Content Licensing [Member]
Disaggregation of Revenue [Line Items]
Revenue	648	684	1,381	1,418
Filmed Entertainment [Member] | Home Entertainment [Member]
Disaggregation of Revenue [Line Items]
Revenue	225	334	473	620
Filmed Entertainment [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	297	287	540	583
Theme Parks [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,361	1,314	2,642	2,432
NBCUniversal Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,313	8,318	17,843	16,171
Corporate, Non-Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue	255	205	646	413
Corporate, Non-Segment [Member] | NBCUniversal Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	15	9	29	17
Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(543)	(494)	(1,191)	(1,018)
Eliminations [Member] | NBCUniversal Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	(80)	(84)	(183)	(172)
NBCUniversal Media LLC [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,313	8,318	17,843	16,171
NBCUniversal Media LLC [Member] | Cable Networks [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,916	2,696	6,110	5,336
NBCUniversal Media LLC [Member] | Cable Networks [Member] | Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,684	1,550	3,571	3,112
NBCUniversal Media LLC [Member] | Cable Networks [Member] | Advertising [Member]
Disaggregation of Revenue [Line Items]
Revenue	938	906	1,926	1,732
NBCUniversal Media LLC [Member] | Cable Networks [Member] | Content Licensing And Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	294	240	613	492
NBCUniversal Media LLC [Member] | Broadcast Television [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,391	2,241	5,888	4,449
NBCUniversal Media LLC [Member] | Broadcast Television [Member] | Advertising [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,387	1,270	3,752	2,549
NBCUniversal Media LLC [Member] | Broadcast Television [Member] | Content Licensing [Member]
Disaggregation of Revenue [Line Items]
Revenue	481	523	1,003	1,026
NBCUniversal Media LLC [Member] | Broadcast Television [Member] | Distribution And Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	523	448	1,133	874
NBCUniversal Media LLC [Member] | Filmed Entertainment [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,710	2,142	3,357	4,109
NBCUniversal Media LLC [Member] | Filmed Entertainment [Member] | Theatrical [Member]
Disaggregation of Revenue [Line Items]
Revenue	540	837	963	1,488
NBCUniversal Media LLC [Member] | Filmed Entertainment [Member] | Content Licensing [Member]
Disaggregation of Revenue [Line Items]
Revenue	648	684	1,381	1,418
NBCUniversal Media LLC [Member] | Filmed Entertainment [Member] | Home Entertainment [Member]
Disaggregation of Revenue [Line Items]
Revenue	225	334	473	620
NBCUniversal Media LLC [Member] | Filmed Entertainment [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	297	287	540	583
NBCUniversal Media LLC [Member] | Theme Parks [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,361	1,314	2,642	2,432
NBCUniversal Media LLC [Member] | Corporate, Non-Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue	15	9	29	17
NBCUniversal Media LLC [Member] | Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (80)	$ (84)	$ (183)	$ (172)

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