Derivatives and Risk Management (Balance Sheet Classification of Derivative Financial Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative assets	$ 274	$ 387
Derivative liabilities	1,256	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	3	1
Natural Gas | Fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	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	158	7
Natural Gas | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	52	3
Natural Gas | Two-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	16	54
Natural Gas | Two-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	12	20
Natural Gas | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	151	43
Natural Gas | Two-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	27	21
Natural Gas | Three-way costless collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	18	57
Natural Gas | Three-way costless collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	68	87
Natural Gas | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	217	82
Natural Gas | Three-way costless collars | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	158	102
Natural Gas | Basis swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	83	60
Natural Gas | Basis swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	56	15
Natural Gas | Basis swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	19	3
Natural Gas | Basis swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	8	7
Natural Gas | Call options | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	9	4
Natural Gas | Call options | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	51	12
Natural Gas | Call options | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	31	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	5	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	58	12
Oil | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	22	2
Oil | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	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	5	15
Oil | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	29	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
Ethane | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	21	10
Ethane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	0
Ethane | Two-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	0
Propane | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	110	36
Propane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	16	2
Propane | Three-way costless collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	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	36	8
Normal Butane | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	7	1
Natural Gasoline | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	39	13
Natural Gasoline | Fixed price swaps | Long-term derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	7	2
Natural Gas Storage | Purchased fixed price swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	0
Natural Gas Storage | Fixed price swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ 2	$ 0