Regulatory Matters - Other Regulatory Matters (Details) customer in Thousands, $ in Millions	1 Months Ended				6 Months Ended		12 Months Ended			36 Months Ended
	Jul. 31, 2021 USD ($)	Nov. 30, 2020 USD ($) claim	Aug. 31, 2020 customer	Jul. 31, 2019 USD ($) customer	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2022 USD ($)
Public Utilities, General Disclosures [Line Items]
Other Customer-Provided Capital rate					1.80%	2.65%
Return on regulatory assets					$ 1,849.0		$ 1,696.0
Recovery period for deferred derivative losses					3 years
CECONY | Commodity
Public Utilities, General Disclosures [Line Items]
Recovery period					4 years
CECONY | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets					$ 1,656.0		1,509.0
CECONY | NYSPSC | Manhattan Steam Main Rupture | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Property damage, clean up and response expense					17.0
Capital and retirement costs					9.0
Loss contingency accrual						$ 3.0
CECONY | NYSPSC | Steam | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA									$ 15.0
Impact in regulatory liability resulting from TCJA									$ 185.0
Tax credit, amortization period									3 years
CECONY | Electric | West Side of Manhattan | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer			190	72
Estimate of possible loss (up to)				$ 24.8
CECONY | Electric | Brooklyn
Public Utilities, General Disclosures [Line Items]
Revenues, negative adjustment								$ 15.0
CECONY | Electric | Brooklyn | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer				30
CECONY | Electric | Tropical Storm | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer			330
Estimate of possible loss (up to)		$ 102.3
Restoration costs					174.0
Operation and maintenance expenses charged against a storm reserve					84.0
Capital expenditures					63.0
Operation and maintenance expenses					27.0
Food and medicine spoilage expense					$ 7.5
Alleged number of claims, violations | claim		33
Litigation settlement, period					35 years
CECONY | Electric | Tropical Storm | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	$ 75.1
CECONY | Electric | Tropical Storm | Foregone Customer Recovery | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	25.0
CECONY | Electric | Tropical Storm | Ongoing Operations And Maintenance Costs | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	15.8
CECONY | Electric | Tropical Storm | Costs To Reimburse Customers For Food And Medicine Spoilage | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	14.3
CECONY | Electric | Tropical Storm | Previously Incurred Or Accrued Costs | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	34.3
CECONY | Electric | Rainey Outages | Negative Revenue Adjustment | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	5.0
CECONY | Electric | 2019 Manhattan and Brooklyn Outages | Negative Revenue Adjustment | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	15.0
CECONY | Electric | Scenario, Forecast | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA										$ 377.0
TCJA, net benefit amortization, allocation period										3 years
CECONY | Electric | Scenario, Forecast | Protected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA										$ 1,663.0
CECONY | Electric | Scenario, Forecast | Unprotected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
TCJA, net benefit amortization, allocation period										5 years
Impact in regulatory liability resulting from TCJA										$ 784.0
CECONY | Gas | Scenario, Forecast | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA										$ 63.0
TCJA, net benefit amortization, allocation period										2 years
CECONY | Gas | Scenario, Forecast | Protected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA										$ 725.0
CECONY | Gas | Scenario, Forecast | Unprotected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
TCJA, net benefit amortization, allocation period										5 years
Impact in regulatory liability resulting from TCJA										$ 107.0
O&R | Electric | Tropical Storm | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer			200
Property damage, clean up and response expense					$ 1.6
Estimate of possible loss (up to)		$ 19.0
Restoration costs					26.5
Operation and maintenance expenses charged against a storm reserve					19.2
Capital expenditures					5.7
Alleged number of claims, violations | claim		38
O&R | Electric | Tropical Storm | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	7.0
O&R | Electric | Tropical Storm | Foregone Customer Recovery | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	2.5
O&R | Electric | Tropical Storm | Ongoing Operations And Maintenance Costs | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	2.9
O&R | Electric | Tropical Storm | Previously Incurred Or Accrued Costs | Subsequent Event | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount	$ 1.6
O&R | Electric and Gas Transmission Projects | Scenario, Forecast | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA										$ 22.0
TCJA, net benefit amortization, allocation period										3 years
O&R | Electric and Gas Transmission Projects | Scenario, Forecast | Protected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA										$ 123.0
O&R | Electric and Gas Transmission Projects | Scenario, Forecast | Unprotected Portion | Subsidiaries
Public Utilities, General Disclosures [Line Items]
TCJA, net benefit amortization, allocation period										15 years
Impact in regulatory liability resulting from TCJA										$ 30.0
RECO | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets					26.0		$ 31.0
RECO | Electric | Tropical Storm | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Restoration costs					10.8
Operation and maintenance expenses charged against a storm reserve					7.5
Capital expenditures					2.0
Food and medicine spoilage expense					$ 1.3