Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Related Party Transaction [Line Items]
Revenue	$ 26,827		$ 22,135		$ 80,544	$ 66,661
Total costs and expenses	(21,487)		(17,299)		(64,666)	(52,166)
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	8,294		8,625		24,866	26,468
Total costs and expenses	$ (6,742)		(6,932)		$ (19,698)	(21,393)
Comcast and Consolidated Subsidiaries [Member] | NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue		$ 597	506	$ 1,808		1,580
Total costs and expenses		(73)	(59)	(198)		(162)
Interest expense and investment and other income (loss), net		$ (162)	$ (9)	$ (148)		$ (52)