Commitments, Guarantees and Contingencies - Potential Collateral Obligations (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 351
Curing period	30 days
At Current Credit Rating
Guarantor Obligations [Line Items]
Guarantor obligations	$ 1
Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	40
Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	310
Utilities and FET
Guarantor Obligations [Line Items]
Guarantor obligations	103
Utilities and FET | At Current Credit Rating
Guarantor Obligations [Line Items]
Guarantor obligations	0
Utilities and FET | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	40
Utilities and FET | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	63
FirstEnergy
Guarantor Obligations [Line Items]
Guarantor obligations	246
FirstEnergy | At Current Credit Rating
Guarantor Obligations [Line Items]
Guarantor obligations	0
FirstEnergy | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	0
FirstEnergy | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	246
AE Supply
Guarantor Obligations [Line Items]
Guarantor obligations	2
AE Supply | At Current Credit Rating
Guarantor Obligations [Line Items]
Guarantor obligations	1
AE Supply | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	0
AE Supply | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 1