Condensed Consolidating Financial Information (Narrative) (Details) $ in Millions |
Mar. 31, 2017
USD ($)
|
|---|---|
| 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 | $ 3,400 |