Material Contingencies - Con Edison Transmission (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 2,042	$ 1,831
Payment Guarantee by CET Electric of Contributions to New York Transco LLC
Guarantor Obligations [Line Items]
Estimated project cost percentage	175.00%
NY Transco \| Payment Guarantee by CET Electric of Contributions to New York Transco LLC
Guarantor Obligations [Line Items]
Ownership interest, percentage	45.70%

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant