Derivatives and Risk Management (Summary of Before Tax Effect of Fair Value Hedges not Designated for Hedge Accounting) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	$ (56)	$ 173	$ (54)	$ 319
Derivative Instrument, Settled Gain (Loss) on Derivatives	20	(39)	11	(69)
Total gain (loss) on derivatives	(36)	134	(43)	250
Sold Fixed Price Swaps [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(26)	58	(29)	176
Derivative Instrument, Settled Gain (Loss) on Derivatives	13	(9)	13	(25)
Sold Fixed Price Swaps [Member] | Propane [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(12)		(9)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)		(1)
Sold Fixed Price Swaps [Member] | Ethane [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(2)		(2)
Two-Way Costless Collars [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(1)	14	2	45
Derivative Instrument, Settled Gain (Loss) on Derivatives			4	(3)
Three-Way Costless Collars [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(24)	31	(29)	88
Derivative Instrument, Settled Gain (Loss) on Derivatives	12	(1)	19	(5)
Sold Basis Swaps [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(4)	60	16	(43)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(3)	(29)	(24)	(30)
Purchased Call Options [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(12)		4
Derivative Instrument, Settled Gain (Loss) on Derivatives			2	(6)
Sold Call Options [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	31	11	(3)	53
Derivative Instrument, Settled Gain (Loss) on Derivatives			(1)
Amortization of premium paid			1
Sold Call Options [Member] | Oil [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(6)		(6)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)		(1)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives		(1)	2
Derivative Instrument, Settled Gain (Loss) on Derivatives