Derivative Instruments and Hedging Activities (Fair Values) (Details) - USD ($) $ in Millions |
Sep. 30, 2015 |
Dec. 31, 2014 |
---|---|---|
Fair Values by Balance Sheet Location [Abstract] | ||
Asset value | $ 802 | $ 1,318 |
Liability value | 684 | 1,217 |
Not Designated as Hedging Instrument | ||
Fair Values by Balance Sheet Location [Abstract] | ||
Asset value | 802 | 1,318 |
Liability value | 684 | 1,217 |
Not Designated as Hedging Instrument | Current Assets | Energy Commodities, net | ||
Fair Values by Balance Sheet Location [Abstract] | ||
Asset value | 576 | 1,079 |
Not Designated as Hedging Instrument | Noncurrent Assets | Energy Commodities, net | ||
Fair Values by Balance Sheet Location [Abstract] | ||
Asset value | 226 | 239 |
Not Designated as Hedging Instrument | Current Liabilities | Energy Commodities, net | ||
Fair Values by Balance Sheet Location [Abstract] | ||
Liability value | 506 | 1,024 |
Not Designated as Hedging Instrument | Noncurrent Liabilities | Energy Commodities, net | ||
Fair Values by Balance Sheet Location [Abstract] | ||
Liability value | $ 178 | $ 193 |