Condensed Consolidating Financial Information (Narrative) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	$ 52,900
Maturing In Next Five Years [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	12,300
NBCUniversal Enterprise Senior Debt Securities [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	3,300
Comcast Holdings' ZONES due October 2029 [Member]
Debt Instrument [Line Items]
Principal amount of debt securities subject to guarantee	185
Comcast Holdings' ZONES due November 2029 [Member]
Debt Instrument [Line Items]
Principal amount of debt securities not subject to guarantee	62
Universal Studios Japan Term Loans [Member]
Debt Instrument [Line Items]
Principal amount of debt securities not subject to guarantee	$ 3,300