Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share
Excluded shares from diluted EPS because their inclusion would have an antidilutive effect	26	32
Net income attributable to Comcast Corporation	$ 1,224	$ 943
Basic shares attributable to Comcast Corporation shareholders	2,708	2,772
Assumed exercise or issuance of shares relating to stock plans	36	33
Diluted shares attributable to Comcast Corporation shareholders	2,744	2,805
Basic earnings per common share attributable to Comcast Corporation shareholders	$ 0.45	$ 0.34
Diluted earnings per common share attributable to Comcast Corporation shareholders	$ 0.45	$ 0.34