Environmental Matters - Environmental Remediation Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 5	$ 3	$ 13	$ 8
CECONY \| Subsidiaries
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 5	$ 3	$ 13	$ 8

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109237650&loc=d3e13064-110858

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

Name:	us-gaap_EnvironmentalRemediationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration