Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debtor Obligations [Abstract]
Liabilities subject to compromise, carrying value	$ 2,932	$ 0
Debt outstanding	4,595	4,343
Carrying Amount
Debtor Obligations [Abstract]
Debtor-in-possession (DIP) credit facility, carrying value	148	0
Liabilities subject to compromise, carrying value	2,780	0
Current portion of long-term debt, carrying value	1,815	58
Long-term debt, carrying value	0	4,380
Derivative instruments	9	114
Fair Value
Debtor Obligations [Abstract]
Debtor-in-possession (DIP) credit facility, fair value	148	0
Liabilities subject to compromise, fair value	53	0
Current portion of long-term debt, fair value	1,285	44
Long-term debt, fair value	0	2,532
Derivative instruments	9	114
Reserve-Based Loan Facility due November 23, 2021 \| Line of Credit
Debtor Obligations [Abstract]
Debt outstanding	$ 315	$ 100

Debtor-In-Possession Financing, Letters Of Credit Outstanding, Fair Value Disclosure

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Debtor Obligations [Abstract]

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Liabilities Subject To Compromise, Fair Value Disclosure

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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Amount of letters of credit outstanding under debtor-in-possession financing arrangement.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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Total amount of liabilities subject to compromise.

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