Amount of Gain Loss Recognized in Income Related to Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Realized Gain (Loss) on Derivatives	$ (20)	$ 7	$ (106)	$ 42
Unrealized Gain (Loss) on Derivatives	323	(106)	139	(108)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	303	(99)	33	(66)
Natural gas contracts [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Realized Gain (Loss) on Derivatives	(2)	19	(36)	51
Unrealized Gain (Loss) on Derivatives	38	(6)	30	(24)
Oil contracts [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Realized Gain (Loss) on Derivatives	(18)	(12)	(70)	(9)
Unrealized Gain (Loss) on Derivatives	$ 285	$ (100)	$ 109	$ (84)