Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12021-110248

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

Commitments And Contingent Liabilities (Regulatory Proceedings) (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Jan. 31, 2021	Dec. 31, 2020
Maximum [Member] \| Sewaren 7 Claim [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 68.0	$ 93.0
Maximum [Member] \| LIPA complaint
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 70.0
Minimum \| LIPA complaint
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 7.0