Employee Benefit Plans (Deferred Compensation Plans) (Details) - Deferred Compensation Plans [Member] - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Benefit obligation | $ 2,885 | $ 2,539 | $ 2,164 |
| Interest expense | 222 | 209 | 178 |
| NBCUniversal Media LLC [Member] | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Benefit obligation | 719 | 621 | 494 |
| Interest expense | $ 58 | $ 64 | $ 48 |