Condensed Consolidated Statement of Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 30,298	$ 25,532	$ 86,049	$ 75,856
Costs and Expenses:
Programming and production	10,395	8,565	28,570	23,683
Other operating and administrative	8,981	8,059	25,799	23,959
Advertising, marketing and promotion	1,995	1,512	5,462	4,791
Depreciation	2,177	2,122	6,407	6,328
Amortization	1,301	1,198	3,815	3,520
Total costs and expenses	24,848	21,456	70,053	62,281
Operating income	5,450	4,076	15,996	13,575
Interest expense	(1,050)	(1,220)	(3,161)	(3,544)
Investment and other income (loss), net	766	(86)	2,374	(382)
Income before income taxes	5,166	2,770	15,208	9,649
Income tax expense	(1,235)	(739)	(4,354)	(2,385)
Net income	3,931	2,031	10,854	7,264
Less: Net income (loss) attributable to noncontrolling interests and redeemable subsidiary preferred stock	(104)	12	(249)	110
Net income attributable to Comcast Corporation	$ 4,035	$ 2,019	$ 11,102	$ 7,154
Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.88	$ 0.44	$ 2.42	$ 1.57
Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.86	$ 0.44	$ 2.38	$ 1.55