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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (229)	$ 118	$ 17	$ 96
Settled Gain (Loss) on Derivatives Recognized in Earnings	120	34	213	24
Total gain (loss) on derivatives	(109)	152	230	120
Purchased fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0	0	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0	(2)	0
Purchased fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	7	1	2	5
Settled Gain (Loss) on Derivatives Recognized in Earnings	(4)	(1)	(4)	(2)
Purchased fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0	1	0
Purchased fixed price swaps | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	0	(1)	0
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(39)	57	64	55
Settled Gain (Loss) on Derivatives Recognized in Earnings	84	14	89	8
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(46)	5	72	(8)
Settled Gain (Loss) on Derivatives Recognized in Earnings	22	2	31	4
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(22)	0	(10)	7
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	5	7	6
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(44)	13	(8)	9
Settled Gain (Loss) on Derivatives Recognized in Earnings	7	7	17	9
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(7)	10	(11)	9
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	3	6	2
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(10)	4	9	(3)
Settled Gain (Loss) on Derivatives Recognized in Earnings	6	1	9	2
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(3)	2	(1)	2
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0	2	0
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(45)	22	(96)	24
Settled Gain (Loss) on Derivatives Recognized in Earnings	7	8	43	4
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(6)	1	19	1
Settled Gain (Loss) on Derivatives Recognized in Earnings	3	0	4	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(13)	4	(14)	(6)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(7)	(4)	9	(8)
Purchased call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	3	(2)	4	(2)
Amortization of premium paid	4		4
Sold call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(7)	4	(13)	6
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)	0	(1)
Sold call options | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	0	1	0
Purchased fixed price swaps – storage | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	(1)	0	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	0	1	0
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ 1	$ (2)	$ 0	$ (2)