Derivatives and Risk Management (Balance Sheet Classification of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative assets	$ 350	$ 391
Derivative liabilities	475	236
Natural Gas | Fixed price swaps
Derivatives, Fair Value [Line Items]
Premium paid	1	9
Natural Gas | Three-way costless collars
Derivatives, Fair Value [Line Items]
Deferred premiums	3
Natural Gas | Not Designated as Hedging Instrument | Purchased fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	3	0
Natural Gas | Not Designated as Hedging Instrument | Purchased fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	1
Natural Gas | Not Designated as Hedging Instrument | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	21	77
Premium paid	1	9
Natural Gas | Not Designated as Hedging Instrument | Fixed price swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	7
Natural Gas | Not Designated as Hedging Instrument | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	15	1
Natural Gas | Not Designated as Hedging Instrument | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	6	0
Natural Gas | Not Designated as Hedging Instrument | Two-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	27	10
Natural Gas | Not Designated as Hedging Instrument | Two-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	13	4
Natural Gas | Not Designated as Hedging Instrument | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	52	4
Natural Gas | Not Designated as Hedging Instrument | Two-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	27	4
Natural Gas | Not Designated as Hedging Instrument | Three-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	64	126
Natural Gas | Not Designated as Hedging Instrument | Three-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	56	74
Natural Gas | Not Designated as Hedging Instrument | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	164	84
Deferred premiums	3
Natural Gas | Not Designated as Hedging Instrument | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	106	72
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	40	17
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	13	15
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	3	17
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	9
Natural Gas | Not Designated as Hedging Instrument | Call options | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	9	1
Natural Gas | Not Designated as Hedging Instrument | Call options | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	4	2
Natural Gas | Not Designated as Hedging Instrument | Call options | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	24	3
Natural Gas | Not Designated as Hedging Instrument | Call options | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	29	15
Oil | Not Designated as Hedging Instrument | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	42	4
Oil | Not Designated as Hedging Instrument | Fixed price swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	10	1
Oil | Not Designated as Hedging Instrument | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	6
Oil | Not Designated as Hedging Instrument | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	2
Oil | Not Designated as Hedging Instrument | Two-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	6	5
Oil | Not Designated as Hedging Instrument | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	5
Oil | Not Designated as Hedging Instrument | Three-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	19	3
Oil | Not Designated as Hedging Instrument | Three-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	14	7
Oil | Not Designated as Hedging Instrument | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	10	4
Oil | Not Designated as Hedging Instrument | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	10	8
Oil | Not Designated as Hedging Instrument | Call options | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	1
Ethane | Not Designated as Hedging Instrument | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	2	11
Ethane | Not Designated as Hedging Instrument | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	10	0
Ethane | Not Designated as Hedging Instrument | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	0
Propane | Not Designated as Hedging Instrument | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	5	21
Propane | Not Designated as Hedging Instrument | Fixed price swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	3
Propane | Not Designated as Hedging Instrument | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	5	0
Propane | Not Designated as Hedging Instrument | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	0
Propane | Not Designated as Hedging Instrument | Two-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	2
Natural Gas Storage | Not Designated as Hedging Instrument | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	1
Natural Gas Storage | Not Designated as Hedging Instrument | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ 1	$ 0