Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Energy Holdings [Member]
Schedule of Financial Receivables [Line Items]
Leveraged Leases, Net Investment in Leveraged Leases Disclosure, Investment in Leveraged Leases, Net	$ 169	$ 186
Shawville Station [Member]
Schedule of Financial Receivables [Line Items]
Leveraged Leases, Net Investment in Leveraged Leases Disclosure, Investment in Leveraged Leases, Net	18
Lease Receivable Gross Investment	$ 23

The net investment in arrangements meeting the criteria for classification as leveraged leases including deferred taxes.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 50
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121579104&loc=SL77920254-209983

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 30
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121556109&loc=d3e42840-112730

Name:	us-gaap_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureInvestmentInLeveragedLeasesNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant