Commitments, Guarantees and Contingencies - Potential Collateral Obligations (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 370
Curing period	30 days
Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	$ 47
Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	323
Utilities and FET
Guarantor Obligations [Line Items]
Guarantor obligations	113
Utilities and FET | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	47
Utilities and FET | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	66
FirstEnergy
Guarantor Obligations [Line Items]
Guarantor obligations	257
FirstEnergy | Upon Further Downgrade
Guarantor Obligations [Line Items]
Guarantor obligations	0
FirstEnergy | Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Guarantor obligations	$ 257