Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Earnings Per Share [Abstract]
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 EPS attributable to Comcast Corporation shareholders (in shares)									4,548	4,584	4,708
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
Effect of dilutive securities:
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
Assumed exercise or issuance of shares relating to stock plans (in shares)									62	56	78
Diluted EPS attributable to Comcast Corporation shareholders (in shares)									4,610	4,640	4,786
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