Goodwill and Intangible Assets (Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Schedule of Indefinite and Finite-Lived Intangible Assets [Line Items]
Total	$ 111,917	$ 89,448
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(14,194)	(11,951)
Franchise Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	59,365	59,364
Trade Names [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	9,633	2,981
FCC Licenses [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,333	2,238	$ 1,700
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	16 years
Gross Carrying Amount	$ 25,046	13,612
Accumulated Amortization	$ (6,682)	(5,819)
Software [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	5 years
Gross Carrying Amount	$ 11,395	8,258
Accumulated Amortization	$ (5,990)	(4,846)
Patents and other technology rights [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	7 years
Gross Carrying Amount	$ 260	259
Accumulated Amortization	$ (234)	(221)
Other agreements and rights [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	18 years
Gross Carrying Amount	$ 3,885	2,736
Accumulated Amortization	(1,288)	(1,065)
NBCUniversal Media LLC [Member]
Schedule of Indefinite and Finite-Lived Intangible Assets [Line Items]
Total	22,256	20,891
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(8,590)	(7,585)
NBCUniversal Media LLC [Member] | Trade Names [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	2,981	2,981
NBCUniversal Media LLC [Member] | FCC Licenses [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 608	513
NBCUniversal Media LLC [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	19 years
Gross Carrying Amount	$ 13,269	13,301
Accumulated Amortization	$ (6,283)	(5,643)
NBCUniversal Media LLC [Member] | Software [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	5 years
Gross Carrying Amount	$ 1,779	1,516
Accumulated Amortization	$ (932)	(737)
NBCUniversal Media LLC [Member] | Other agreements and rights [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Original Useful Life	19 years
Gross Carrying Amount	$ 3,619	2,580
Accumulated Amortization	$ (1,375)	$ (1,205)