Regulatory Matters - Other Regulatory Matters (Details) customer in Thousands, $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended	12 Months Ended		36 Months Ended
	Nov. 30, 2020 USD ($) claim	Aug. 31, 2020 customer	Jul. 31, 2019 USD ($) customer	Mar. 31, 2021 USD ($)	Mar. 31, 2020	Sep. 30, 2018 USD ($)	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				$ 1,785.0			$ 1,696.0
CECONY
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets				1,590.0			1,509.0
CECONY | NYSPSC | Manhattan Steam Main Rupture
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
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
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer			72
Estimate of possible loss			$ 24.8
CECONY | Electric | Brooklyn
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer			30
Revenues, negative adjustment								$ 15.0
CECONY | Electric | Tropical Storm
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer		330
Estimate of possible loss	$ 102.3
Operation and maintenance expenses charged against a storm reserve				87.0
Restoration costs				172.0
Operation and maintenance expenses				22.0
Capital expenditures				63.0
Food and medicine spoilage expense				7.5
Alleged number of claims, violations | claim	33
CECONY | Electric | Scenario, Forecast
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
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									$ 1,663.0
CECONY | Electric | Scenario, Forecast | Unprotected Portion
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
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
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									$ 725.0
CECONY | Gas | Scenario, Forecast | Unprotected Portion
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
Public Utilities, General Disclosures [Line Items]
Property damage, clean up and response expense				2.9
Number of customers affected with interrupted service | customer		200
Estimate of possible loss	$ 19.0
Operation and maintenance expenses charged against a storm reserve				29.0
Restoration costs				37.0
Capital expenditures				8.0
Alleged number of claims, violations | claim	38
O&R | Electric and Gas Transmission Projects | Scenario, Forecast
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
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
Public Utilities, General Disclosures [Line Items]
TCJA, net benefit amortization, allocation period									15 years
Impact in regulatory liability resulting from TCJA									$ 30.0
RECO
Public Utilities, General Disclosures [Line Items]
Return on regulatory assets				$ 27.0			$ 31.0