RELATED-PARTY TRANSACTIONS - Schedule of Expenses Incurred By Holdings From Services Provided By Affiliated Company (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Related Party Transactions [Abstract]
Expenses incurred	$ 68	$ 60	$ 138	$ 109

Expenses Incurred By Company From Services Provided By Affiliates

No definition available.

Name:	cik0000914748_ExpensesIncurredByCompanyFromServicesProvidedByAffiliates
Namespace Prefix:	cik0000914748_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration