Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Aggregate Principal Amount of Current and Long-Term Debt	$ 4,890	$ 5,640
Estimated Fair Value of Debt	5,609	6,505
Commodity Contract [Member] \| Crude Oil \| Price Swaps
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	226
Commodity Contract [Member] \| Crude Oil \| Price Swaps \| Fair Value, Inputs, Level 1 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Commodity Contract [Member] \| Crude Oil \| Price Swaps \| Fair Value, Inputs, Level 2 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	226
Commodity Contract [Member] \| Crude Oil \| Price Swaps \| Fair Value, Inputs, Level 3 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Commodity Contract [Member] \| Crude Oil \| Roll Differential Swap
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	32	1
Commodity Contract [Member] \| Crude Oil \| Roll Differential Swap \| Fair Value, Inputs, Level 1 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Commodity Contract [Member] \| Crude Oil \| Roll Differential Swap \| Fair Value, Inputs, Level 2 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	32	1
Commodity Contract [Member] \| Crude Oil \| Roll Differential Swap \| Fair Value, Inputs, Level 3 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Commodity Contract [Member] \| Natural Gas Liquids \| Price Swaps
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	43
Commodity Contract [Member] \| Natural Gas Liquids \| Price Swaps \| Fair Value, Inputs, Level 1 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Commodity Contract [Member] \| Natural Gas Liquids \| Price Swaps \| Fair Value, Inputs, Level 2 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	43
Commodity Contract [Member] \| Natural Gas Liquids \| Price Swaps \| Fair Value, Inputs, Level 3 [Member]
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Commodity Contract [Member] \| Natural Gas \| Price Swaps
Financial Assets: [Abstract]
Assets, Fair Value Disclosure	21	66
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	329
Commodity Contract [Member] \| Natural Gas \| Price Swaps \| Fair Value, Inputs, Level 1 [Member]
Financial Assets: [Abstract]
Assets, Fair Value Disclosure	0	0
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Commodity Contract [Member] \| Natural Gas \| Price Swaps \| Fair Value, Inputs, Level 2 [Member]
Financial Assets: [Abstract]
Assets, Fair Value Disclosure	21	66
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	329
Commodity Contract [Member] \| Natural Gas \| Price Swaps \| Fair Value, Inputs, Level 3 [Member]
Financial Assets: [Abstract]
Assets, Fair Value Disclosure	0	$ 0
Financial Liabilities:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value of financial and nonfinancial obligations.

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