Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Revenue	$ 28,398	$ 26,827	$ 26,858	$ 26,859	$ 27,846	$ 22,135	$ 21,735	$ 22,791	$ 108,942	$ 94,507	$ 85,029
Total costs and expenses									(87,817)	(75,498)	(67,011)
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue									34,021	35,895	32,950
Total costs and expenses									(27,395)	(29,229)	(26,473)
Comcast and Consolidated Subsidiaries [Member] | NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue									2,398	2,156	1,837
Total costs and expenses									(287)	(245)	(214)
Interest expense and investment and other income (loss), net									$ (133)	$ (54)	$ (250)