General - Devaluation (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
Foreign exchange related charges | $ 11 | $ 0 | $ 37 | $ 0 |
Angola, Kwanza | ||||
Foreign exchange related charges | $ 11 | $ 35 |