Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 28,398	$ 26,827	$ 26,858	$ 26,859	$ 27,846	$ 22,135	$ 21,735	$ 22,791	$ 108,942	$ 94,507	$ 85,029
Operating income	5,247	5,340	5,356	5,182	4,514	4,836	5,014	4,645	21,125	19,009	18,018
Net income attributable to Comcast Corporation	$ 3,162	$ 3,217	$ 3,125	$ 3,553	$ 2,511	$ 2,886	$ 3,216	$ 3,118	$ 13,057	$ 11,731	$ 22,735
Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.69	$ 0.71	$ 0.69	$ 0.78	$ 0.55	$ 0.63	$ 0.70	$ 0.67	$ 2.87	$ 2.56	$ 4.83
Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	0.68	0.70	0.68	0.77	0.55	0.62	0.69	0.66	2.83	2.53	4.75
Dividends declared per common share (in dollars per share)	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.19	$ 0.19	$ 0.19	$ 0.19	$ 0.84	$ 0.76	$ 0.63