Derivative Instruments - Summary of Derivative Activity (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement Impact of Derivative Activity [Abstract]
Gain (loss) on derivative instruments not designated as hedging instruments	$ 50	$ (60)	$ (292)
Derivative, Credit Risk Related Contingent Features [Abstract]
Aggregate fair value of derivatives with credit-risk-related contingent features in a liability position	14	20
Fair value of collateral already posted	7	7
Additional collateral required to be posted if credit risk contingent features triggered (1)	7	3
Gains (Losses) in Other Income (Expense) \| Indexed debt securities derivative
Income Statement Impact of Derivative Activity [Abstract]
Gain (loss) on derivative instruments not designated as hedging instruments	50	(60)	$ (292)
Not Designated as Hedging Instrument
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	14	0
Derivative Liabilities Fair Value	917	983
Not Designated as Hedging Instrument \| Current Assets \| Natural gas derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	9	0
Derivative Liabilities Fair Value	0	0
Not Designated as Hedging Instrument \| Other Noncurrent Assets \| Natural gas derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	5	0
Derivative Liabilities Fair Value	0	0
Not Designated as Hedging Instrument \| Current Liabilities \| Natural gas derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	0	0
Derivative Liabilities Fair Value	0	3
Not Designated as Hedging Instrument \| Current Liabilities \| Interest rate derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	0	0
Derivative Liabilities Fair Value	2	0
Not Designated as Hedging Instrument \| Current Liabilities \| Indexed debt securities derivative
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	0	0
Derivative Liabilities Fair Value	903	953
Not Designated as Hedging Instrument \| Other Noncurrent Liabilities \| Natural gas derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	0	0
Derivative Liabilities Fair Value	0	7
Not Designated as Hedging Instrument \| Other Noncurrent Liabilities \| Interest rate derivatives
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Derivative Assets Fair Value	0	0
Derivative Liabilities Fair Value	$ 12	$ 20

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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