Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Net Investments in Leases	$ 186	$ 169
Shawville Station [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Counterparties' S&P Credit Ratings	BB+
Merrill Creek Reservoir [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Investments in Leases	$ 20
Lease Receivable, Counterparty	Metropolitan Edison Company (a subsidiary of First Energy)
Lease Receivable, Gross Investment	$ 26