Derivatives and Risk Management (Summary of Before Tax Effect of Cash Flow Hedges on Consolidated Financial Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (138)	$ 94
Settled Gain (Loss) on Derivatives Recognized in Earnings	362	180
Total gain (loss) on derivatives	224	274
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(25)	46
Settled Gain (Loss) on Derivatives Recognized in Earnings	142	78
Amortization of premium paid	9
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(22)
Settled Gain (Loss) on Derivatives Recognized in Earnings	65	10
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(21)	6
Settled Gain (Loss) on Derivatives Recognized in Earnings	6	17
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(60)	13
Settled Gain (Loss) on Derivatives Recognized in Earnings	18	29
Fixed price swaps | Normal Butane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(9)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(2)	0
Fixed price swaps | Natural Gasoline
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(15)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Fixed price swaps | Natural gas storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	1
Settled Gain (Loss) on Derivatives Recognized in Earnings	2	(1)
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	10	2
Settled Gain (Loss) on Derivatives Recognized in Earnings	(5)	16
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	(10)
Settled Gain (Loss) on Derivatives Recognized in Earnings	17	6
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	2
Settled Gain (Loss) on Derivatives Recognized in Earnings	2	2
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(77)	37
Settled Gain (Loss) on Derivatives Recognized in Earnings	38	31
Amortization of premium paid	2
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	3	(2)
Settled Gain (Loss) on Derivatives Recognized in Earnings	9	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	59	17
Settled Gain (Loss) on Derivatives Recognized in Earnings	76	(3)
Call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(10)	1
Amortization of premium paid		1
Call options | Natural Gas | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(2)
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	7	0
Purchased fixed price swaps | Natural Gas | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	2	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	(3)	0
Purchased fixed price swaps | Oil | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	6
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(3)
Purchased fixed price swaps | Natural gas storage | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	$ (1)	$ 0