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
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (169)	$ 246
Settled Gain (Loss) on Derivatives Recognized in Earnings	(22)	93
Total gain (loss) on derivatives	(191)	339
Purchased fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Purchased fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(5)
Purchased fixed price swaps | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(22)	103
Settled Gain (Loss) on Derivatives Recognized in Earnings	5	5
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(40)	118
Settled Gain (Loss) on Derivatives Recognized in Earnings	(17)	9
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(2)	12
Settled Gain (Loss) on Derivatives Recognized in Earnings	(4)	6
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(45)	36
Settled Gain (Loss) on Derivatives Recognized in Earnings	(30)	10
Fixed price swaps | Normal Butane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(15)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(7)	0
Fixed price swaps | Natural Gasoline
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(20)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(9)	0
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(12)	(4)
Settled Gain (Loss) on Derivatives Recognized in Earnings	2	6
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	19
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	3
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	2
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	1
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(51)
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	36
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(18)	25
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	1
Three-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	3	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	41	16
Call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	3	(5)
Call options | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	1
Swaptions | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Fixed price swaps – storage | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	1
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	(1)
Put options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Settled Gain (Loss) on Derivatives Recognized in Earnings	(2)	$ 0
Amortization of premium paid	$ 2