Derivatives and Risk Management (Balance Sheet Classification of Derivative Financial Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Fair value of net derivative liability position decrease	$ 7	$ 1
Derivative assets	237	387
Derivative liabilities	3,735	428
Interest rate swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	0
Natural Gas | Purchased fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	2	1
Natural Gas | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	37
Natural Gas | Fixed price swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	7
Natural Gas | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1,010	7
Natural Gas | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	406	3
Natural Gas | Two-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	11	54
Natural Gas | Two-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	17	20
Natural Gas | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	495	43
Natural Gas | Two-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	82	21
Natural Gas | Three-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	13	57
Natural Gas | Three-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	41	87
Natural Gas | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	650	82
Natural Gas | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	313	102
Natural Gas | Basis swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	66	60
Natural Gas | Basis swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	44	15
Natural Gas | Basis swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	48	3
Natural Gas | Basis swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	20	7
Natural Gas | Call options | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	35	4
Natural Gas | Call options | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	182	12
Natural Gas | Call options | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	69	28
Natural Gas | Put options | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	1
Natural Gas | Swaptions | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	26	2
Oil | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	13
Oil | Fixed price swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	2
Oil | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	60	12
Oil | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	20	2
Oil | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	1
Oil | Three-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	15
Oil | Three-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	4	15
Oil | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	28	15
Oil | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	24	15
Oil | Call options | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	0
Natural Gas Storage | Purchased fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	2	0
Natural Gas Storage | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	5	0
Ethane | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	32	10
Ethane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	3	0
Ethane | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	0
Propane | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	143	36
Propane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	15	2
Propane | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	0
Propane | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	0
Normal Butane | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	44	8
Normal Butane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	6	1
Natural Gasoline | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	40	13
Natural Gasoline | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ 5	$ 2