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, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	$ 94	$ (24)
Derivative Instrument, Settled Gain (Loss) on Derivatives	180	(94)
Total gain (loss) on derivatives	274	(118)
Fixed Price Swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	46	(27)
Derivative Instrument, Settled Gain (Loss) on Derivatives	78	(32)
Fixed Price Swaps | Natural Gas | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(1)	0
Fixed Price Swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(22)	19
Derivative Instrument, Settled Gain (Loss) on Derivatives	10	0
Fixed Price Swaps | Oil | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	6	(6)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(3)	0
Fixed Price Swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	13	11
Derivative Instrument, Settled Gain (Loss) on Derivatives	29	(6)
Fixed Price Swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	6	5
Derivative Instrument, Settled Gain (Loss) on Derivatives	17	(8)
Fixed Price Swaps | Natural gas storage
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	1	0
Fixed Price Swaps | Natural gas storage | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)	0
Two-Way Costless Collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	2	0
Derivative Instrument, Settled Gain (Loss) on Derivatives	16	(1)
Two-Way Costless Collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(10)	10
Derivative Instrument, Settled Gain (Loss) on Derivatives	6	0
Two-Way Costless Collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	2	0
Derivative Instrument, Settled Gain (Loss) on Derivatives	2	0
Three-Way Costless Collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	37	(48)
Derivative Instrument, Settled Gain (Loss) on Derivatives	31	(9)
Three-Way Costless Collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(2)	0
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	17	10
Derivative Instrument, Settled Gain (Loss) on Derivatives	(3)	(31)
Call Option | Natural Gas | Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(3)	4
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)	2
Amortization of premium paid	1	1
Call Option | Natural Gas | Sold
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	4	(4)
Derivative Instrument, Settled Gain (Loss) on Derivatives	(1)	(7)
Call Option | Oil | Sold
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	(1)	0
Derivative Instrument, Settled Gain (Loss) on Derivatives	0	(2)
Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Unsettled Gain (Loss) on Derivatives	$ (1)	$ 2