Regulatory Matters - Other Regulatory Matters (Details) customer in Thousands, $ in Millions		1 Months Ended				3 Months Ended	6 Months Ended	9 Months Ended		12 Months Ended		36 Months Ended
	Jan. 01, 2022 USD ($)	Jul. 31, 2021 USD ($)	Nov. 30, 2020 USD ($) claim	Aug. 31, 2020 customer	Jul. 31, 2019 USD ($) customer	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2022 USD ($)
Public Utilities, General Disclosures [Line Items]
Other Customer-Provided Capital rate								1.80%	2.65%
Return on regulatory assets								$ 2,027.0		$ 1,696.0
Recovery period for deferred derivative losses								3 years
CECONY
Public Utilities, General Disclosures [Line Items]
Net regulatory assets								$ 1,180.0		1,200.0
CECONY | Commodity
Public Utilities, General Disclosures [Line Items]
Recovery period								4 years
CECONY | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets								$ 1,817.0		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
Settlement agreement, amount		$ 75.1
Estimate of possible loss (up to)			$ 102.3
Restoration costs								175.0
Operation and maintenance expenses charged against a storm reserve								84.0
Capital expenditures								64.0
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 | Foregone Customer Recovery | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		25.0
CECONY | Electric | Tropical Storm | Ongoing Operations And Maintenance Costs | 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 | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		14.3
CECONY | Electric | Tropical Storm | Previously Incurred Or Accrued Costs | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		34.3
CECONY | Electric | Rainey Outages | Negative Revenue Adjustment | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		5.0
CECONY | Electric | 2019 Manhattan and Brooklyn Outages | Negative Revenue Adjustment | 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
Public Utilities, General Disclosures [Line Items]
Net regulatory assets								$ 26.0		29.0
O&R | Electric | Tropical Storm | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer				200
Settlement agreement, amount		7.0
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 | Foregone Customer Recovery | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		2.5
O&R | Electric | Tropical Storm | Ongoing Operations And Maintenance Costs | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Settlement agreement, amount		2.9
O&R | Electric | Tropical Storm | Previously Incurred Or Accrued Costs | 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	6 years											15 years
Impact in regulatory liability resulting from TCJA	$ 34.0											$ 30.0
RECO | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets								24.0		$ 31.0
RECO | Electric | Tropical Storm | Subsidiaries
Public Utilities, General Disclosures [Line Items]
Restoration costs								11.3
Operation and maintenance expenses charged against a storm reserve								7.5
Capital expenditures								2.5
Food and medicine spoilage expense								$ 1.3