Condensed Consolidating Financial Information (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
	Nov. 13, 2015	Dec. 31, 2015
Comcast Holdings' ZONES due October 2029 [Member]
Debt Instrument, Maturity Date, Description		October 2029
Principal amount of debt securities subject to guarantee		$ 185
Comcast Holdings' ZONES due November 2029 [Member]
Debt Instrument, Maturity Date, Description		November 2029
Principal amount of debt securities not subject to guarantee		$ 62
Guarantor Subsidiaries [Member]
Principal amount of debt securities subject to guarantee		44,300
Maturing In Next Five Years [Member]
Principal amount of debt securities subject to guarantee		$ 10,700
NBCUniversal Enterprise Credit Facility [Member]
Debt Instrument, Maturity Date, Description		March 2018
NBCUniversal Enterprise Senior Debt Securities [Member]
Principal amount of debt securities subject to guarantee		$ 4,000
Universal Studios Japan Term Loans [Member]
Debt Instrument, Maturity Date, Description	November 2020
Principal amount of debt securities not subject to guarantee		$ 3,300