REGULATORY MATTERS - Abandonment Transmission Rate Incentive (Details) - PJM 2024 RTEP Window 1 - Valley Link Transmission Rate	Sep. 09, 2025
Regulatory Matters [Line Items]
Recovery of project abandonment costs (percent)	50.00%
Recovery of project abandonment costs incurred thereafter (percent)	1

Public Utilities, Recovery Of Project Abandonment, Prior To Effective Date Costs, Percentage

No definition available.

Name:	fet_PublicUtilitiesRecoveryOfProjectAbandonmentPriorToEffectiveDateCostsPercentage
Namespace Prefix:	fet_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration