Noncontrolling Interests (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income attributable to Comcast Corporation	$ 1,224	$ 943
Increase in Comcast Corporation additional paid-in capital resulting from the issuance of noncontrolling equity interest	0	1,692
Increase in Comcast Corporation additional paid-in capital resulting from the purchase of noncontrolling interest	2	0
Changes in equity resulting from net income attributable to Comcast Corporation and transfers from (to) noncontrolling interests	$ 1,226	$ 2,635