Derivative and Financial Instruments - Commodity Notional (Details) - Short [Member] - Commodity Contract [Member] - USD ($) $ in Millions |
Jun. 30, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Natural gas and power, Fixed price [Member] | ||
| Trading Activity, Gains and Losses, Net [Line Items] | ||
| Commodity derivatives - volumetric material net exposures | (20) | (5) |
| Natural gas and power, Basis [Member] | ||
| Trading Activity, Gains and Losses, Net [Line Items] | ||
| Commodity derivatives - volumetric material net exposures | (27) | (23) |