Employee Benefit Plans (Information On Our Pension Benefit Plans) (Details) - Postretirement Benefit Plan [Member] - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||
| Benefit obligation | $ 408 | $ 425 |
| Amounts in accumulated other comprehensive income not yet recognized in benefits expense | (439) | (458) |
| NBCUniversal Media LLC [Member] | ||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||
| Benefit obligation | 47 | 51 |
| Amounts in accumulated other comprehensive income not yet recognized in benefits expense | $ (163) | $ (177) |