RESERVES FOR LOSSES AND LAE - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023
Reserves For Losses And LAE [Line Items]
Current year incurred losses	$ 2,801	$ 2,720
Prior year incurred development	20	$ 1
Higher Premiums Earned
Reserves For Losses And LAE [Line Items]
Increase (decrease) in earned premium growth	94
Catastrophe Losses
Reserves For Losses And LAE [Line Items]
Increase (decrease) in earned premium growth	$ (12)

Reserves For Losses And LAE [Line Items]

No definition available.

Name:	cik0000914748_ReservesForLossesAndLaeLineItems
Namespace Prefix:	cik0000914748_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

+ Details

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480046/944-40-55-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

+ Details

Name:	us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

+ References

+ Details

Name:	us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis=cik0000914748_HigherPremiumsEarnedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis=cik0000914748_CatastropheLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: