Derivative Instruments (Details 4) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Summary of Derivative Instruments by Risk Exposure [Abstract]
Gain (Loss) on Derivative Instruments, Net, Pretax	[1]	$ (372)	$ 84
Gain (Loss) on Sale of Derivatives	[2],[3]	(3)	29
Mark-to-market gain (loss)	[4]	(369)	55
Sales [Member]
Summary of Derivative Instruments by Risk Exposure [Abstract]
Gain (Loss) on Derivative Instruments, Net, Pretax	[1],[5],[6]	(359)	223
Cost of Sales [Member]
Summary of Derivative Instruments by Risk Exposure [Abstract]
Gain (Loss) on Derivative Instruments, Net, Pretax	[1],[5],[6]	(15)	(139)
Interest Expense [Member]
Summary of Derivative Instruments by Risk Exposure [Abstract]
Gain (Loss) on Derivative Instruments, Net, Pretax	[1]	2	0
Interest Rate Hedging Instruments
Summary of Derivative Instruments by Risk Exposure [Abstract]
Mark-to-market gain (loss)	[4]	2	0
Energy Related Derivative [Member]
Summary of Derivative Instruments by Risk Exposure [Abstract]
Gain (Loss) on Sale of Derivatives	[2],[3]	(3)	29
Mark-to-market gain (loss)	[4]	$ (371)	$ 55

[1] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes adjustments to reflect changes in credit default risk exposure and hedge ineffectiveness.

[2] Does not include the realized value associated with derivative instruments that settle through physical delivery.

[3] Includes amortization of acquisition date fair value of financial derivative activity related to the acquisition of Champion Energy, Calpine Solutions and North American Power.

[4] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.

[5] Does not include the realized value associated with derivative instruments that settle through physical delivery.

[6] Includes amortization of acquisition date fair value of financial derivative activity related to the acquisition of Champion Energy, Calpine Solutions and North American Power.