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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (772)	$ (229)	$ (941)	$ 17
Settled Gain (Loss) on Derivatives Recognized in Earnings	(99)	120	(121)	213
Total gain (loss) on derivatives	(871)	(109)	(1,062)	230
Purchased fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	2	1	2	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	(1)	1	(2)
Purchased fixed price swaps | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0	1	(1)
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(221)	(39)	(243)	64
Settled Gain (Loss) on Derivatives Recognized in Earnings	(6)	84	(1)	89
Amortization of premium paid		4		4
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(41)	(39)	(81)	74
Settled Gain (Loss) on Derivatives Recognized in Earnings	(28)	18	(45)	27
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(11)	(22)	(13)	(10)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(6)	2	(10)	8
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(43)	(44)	(88)	(8)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(30)	7	(60)	17
Fixed price swaps | Normal Butane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(19)	0	(34)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(9)	0	(16)	0
Fixed price swaps | Natural Gasoline
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(11)	0	(31)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(13)	0	(22)	0
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(148)	(7)	(160)	(11)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(2)	0	0	6
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(10)	(1)	9
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	6	(2)	9
Two-way costless collars | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0	(1)	0
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(3)	0	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	1	0	2
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(249)	(45)	(249)	(96)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(8)	7	(7)	43
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(29)	(6)	(47)	19
Settled Gain (Loss) on Derivatives Recognized in Earnings	(5)	3	(6)	4
Three-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0	(2)	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	44	(13)	47	(14)
Settled Gain (Loss) on Derivatives Recognized in Earnings	8	(7)	49	9
Call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(40)	(4)	(37)	(9)
Call options | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	0	(1)	1
Swaptions | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(4)	0	(3)	0
Fixed price swaps – storage | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(2)	1	(2)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	0	0	1
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	1	1	0
Put options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0	1	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	$ 0	$ 0	(2)	$ 0
Amortization of premium paid			$ 2