Segment Information - Narrative (Details) mi² in Thousands, customer in Millions, $ in Billions	9 Months Ended
	Sep. 30, 2019 USD ($) mi² customer company MW
Regulated Distribution
Segment Reporting Information [Line Items]
Number of existing utility operating companies | company	10
Number of customers served by utility operating companies | customer	6
Number of square miles in service area | mi²	65
Megawatts of net demonstrated capacity of competitive segment	3,790
Other/Corporate | OVEC
Segment Reporting Information [Line Items]
Megawatts of net demonstrated capacity of competitive segment	67
FirstEnergy | Other/Corporate
Segment Reporting Information [Line Items]
Long-term debt and other long-term obligations | $	$ 7.1