Financing Receivables (Narrative) (Detail) $ in Millions	3 Months Ended
	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) MW	Dec. 31, 2019 USD ($)
Schedule of Financial Receivables [Line Items]
Pre-Tax Lease write-down	$ 58
Energy Holdings [Member]
Schedule of Financial Receivables [Line Items]
Leveraged Leases, Net Investment in Leveraged Leases Disclosure, Investment in Leveraged Leases, Net		$ 186	$ 169
Shawville Station [Member]
Schedule of Financial Receivables [Line Items]
Leveraged Leases, Net Investment in Leveraged Leases Disclosure, Investment in Leveraged Leases, Net		4
Lease Receivable Gross Investment		$ 72
Lease Receivable Asset Capacity | MW		596