Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Revenue	$ 20,983	$ 21,319	$ 62,611	$ 59,378
Operating costs and expenses	(16,191)	(16,879)	(48,731)	(46,783)
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	8,014	9,178	24,213	23,142
Operating costs and expenses	(5,909)	(7,477)	(19,048)	(19,009)
Comcast and Consolidated Subsidiaries [Member] | NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	463	522	1,382	1,335
Operating costs and expenses	(38)	(53)	(148)	(157)
Other income (expense)	$ (20)	$ (18)	$ (67)	$ (48)