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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	$ (59)	$ 31	$ (113)	$ 350
Derivative Instrument, Settled Gain (Loss) on Derivatives	(6)	14	5	(55)
Total gain (loss) on derivatives	(65)	45	(108)	295
Sold Fixed Price Swaps [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(17)	(2)	(46)	174
Derivative Instrument, Settled Gain (Loss) on Derivatives	5	7	18	(18)
Sold Fixed Price Swaps [Member] | Propane [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(10)		(19)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(5)		(6)
Sold Fixed Price Swaps [Member] | Ethane [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(27)		(29)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(6)		(6)
Two-Way Costless Collars [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	2	3	4	48
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	(7)	(1)	(36)	87
Derivative Instrument, Settled Gain (Loss) on Derivatives	5	1	24	(4)
Sold Basis Swaps [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(5)	24	11	(19)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(4)	9	(28)	(21)
Purchased Call Options [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(2)		2
Derivative Instrument, Settled Gain (Loss) on Derivatives			2
Amortization of premium paid			1
Sold Call Options [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	5	6	2	59
Derivative Instrument, Settled Gain (Loss) on Derivatives		(3)	(1)	(9)
Amortization of premium paid		3		3
Sold Call Options [Member] | Oil [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	1		(5)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)		(2)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	$ 1	$ 1	$ 3	$ 1