Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net Income Attributable to Comcast Corporation	$ 3,125	$ 3,216	$ 6,678	$ 6,334
Basic EPS attributable to Comcast Corporation shareholders (in shares)	4,547	4,598	4,540	4,616
Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.69	$ 0.70	$ 1.47	$ 1.37
Effect of dilutive securities:
Net Income Attributable to Comcast Corporation	$ 3,125	$ 3,216	$ 6,678	$ 6,334
Assumed exercise or issuance of shares relating to stock plans (in shares)	60	45	60	58
Diluted EPS attributable to Comcast Corporation shareholders (in shares)	4,607	4,643	4,600	4,674
Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.68	$ 0.69	$ 1.45	$ 1.36