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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (289)	$ 12	$ (272)	$ 108
Settled Gain (Loss) on Derivatives Recognized in Earnings	97	88	310	112
Total gain (loss) on derivatives	(192)	100	38	220
Purchased fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	4	0	4	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(2)	0	(4)	0
Purchased fixed price swaps | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0	0	0
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(138)	(19)	(74)	36
Settled Gain (Loss) on Derivatives Recognized in Earnings	61	45	150	53
Amortization of premium paid	4		8
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(20)	8	54	5
Settled Gain (Loss) on Derivatives Recognized in Earnings	17	3	44	5
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(13)	1	(23)	8
Settled Gain (Loss) on Derivatives Recognized in Earnings	(2)	6	6	12
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(17)	10	(25)	19
Settled Gain (Loss) on Derivatives Recognized in Earnings	2	11	19	20
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(34)	(11)	(45)	(2)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(5)	10	1	12
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(5)	0	4	(3)
Settled Gain (Loss) on Derivatives Recognized in Earnings	4	2	13	4
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	1	(2)	3
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	1	2	1
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(98)	3	(194)	27
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	15	43	19
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(4)	3	15	4
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0	5	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	54	12	40	6
Settled Gain (Loss) on Derivatives Recognized in Earnings	20	(3)	29	(11)
Call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(16)	1	(25)	5
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)	0	(2)
Amortization of premium paid				1
Call options | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	0	1	0
Fixed price swaps – storage | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(2)	2	(2)	1
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	(1)	2	(1)
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ 0	$ 1	$ 0	$ (1)