Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Obligations [Abstract]
Liabilities subject to compromise, carrying value	$ 2,932	$ 0
Total debt	4,595	4,343
Liabilities subject to compromise, debt	2,780	0
Carrying Amount
Debt 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
Debt 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
Line of Credit \| Reserve-Based Loan Facility, Due November 2021
Debt Obligations [Abstract]
Total debt	$ 315	$ 100

Debt Obligations [Abstract]

No definition available.

Name:	epe_DebtObligationsAbstract
Namespace Prefix:	epe_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	epe_DebtorInPossessionFinancingLettersOfCreditOutstandingFairValueDisclosure
Namespace Prefix:	epe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liabilities Subject To Compromise, Debt

+ References

No definition available.

+ Details

Name:	epe_LiabilitiesSubjectToCompromiseDebt
Namespace Prefix:	epe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liabilities Subject To Compromise, Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	epe_LiabilitiesSubjectToCompromiseFairValueDisclosure
Namespace Prefix:	epe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Long-Term Debt, Current, Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	epe_OtherLongTermDebtCurrentFairValueDisclosure
Namespace Prefix:	epe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Long-Term Debt, Noncurrent, Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	epe_OtherLongTermDebtNoncurrentFairValueDisclosure
Namespace Prefix:	epe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtorInPossessionFinancingLettersOfCreditOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total amount of liabilities subject to compromise.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6918054&loc=d3e56015-112765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56145-112766

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116635682&loc=d3e55717-112764

+ Details

Name:	us-gaap_LiabilitiesSubjectToCompromise
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt classified as other, payable within one year or the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(20))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_OtherLongTermDebtCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt classified as other, payable after one year or the operating cycle, if longer.

+ References

+ Details

Name:	us-gaap_OtherLongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=epe_ReserveBasedLoanFacilityDueNovember2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: