Derivative and Financial Instruments - Commodity Notional (Details 2) - ft3 / D ft3 / D in Billions |
Mar. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Natural gas and power, Fixed price [Member] | ||
| Trading Activity, Gains and Losses, Net [Line Items] | ||
| Commodity derivatives - volumetric material net exposures | (30) | (31) |
| Natural gas and power, Basis [Member] | ||
| Trading Activity, Gains and Losses, Net [Line Items] | ||
| Commodity derivatives - volumetric material net exposures | 31 | 2 |