Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income attributable to parent	$ 2,513	$ 2,028	$ 5,079	$ 4,162
Basic EPS attributable to Comcast Corporation shareholders (in shares)	4,728	4,839	4,738	4,853
Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.53	$ 0.42	$ 1.07	$ 0.86
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Net income attributable to parent	$ 2,513	$ 2,028	$ 5,079	$ 4,162
Assumed exercise or issuance of shares relating to stock plans (in shares)	81	52	82	55
Diluted EPS attributable to Comcast Corporation shareholders (in shares)	4,809	4,891	4,820	4,908
Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share)	$ 0.52	$ 0.41	$ 1.05	$ 0.85