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
	Apr. 01, 2018 USD ($)	Sep. 30, 2018 USD ($)	Aug. 31, 2018 USD ($)	Mar. 31, 2018 USD ($) customer	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory assets		$ 3,975.0			$ 4,333.0			$ 3,975.0	$ 3,975.0
Utilities
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									325.0
CECONY
Public Utilities, General Disclosures [Line Items]
Regulatory assets		3,595.0			3,925.0			3,595.0	3,595.0
CECONY | Future Income Tax
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA		51.0			3,513.0
CECONY | Accelerated Tax Depreciation Benefits
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									2,593.0
CECONY | Deferred Income Tax Charge, Amortized Over Remaining Life of Asset
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									971.0
CECONY | Electric | Hurricane
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer				209
Restoration costs								125.0
Operation and maintenance expenses								16.0
Operation and maintenance expenses charged against a storm reserve								76.0
Capital expenditures		27.0						27.0	27.0
Removal costs								6.0
O&R | Future Income Tax
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA		7.0			$ 161.0
O&R | Accelerated Tax Depreciation Benefits
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									133.0
O&R | Deferred Income Tax Charge, Amortized Over Remaining Life of Asset
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									35.0
O&R | Electric | Hurricane
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer				93
Restoration costs								44.0
RECO | Electric | Hurricane
Public Utilities, General Disclosures [Line Items]
Number of customers affected with interrupted service | customer				44
Restoration costs								17.0
NYSPSC | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA			$ 2,514.0
NYSPSC | CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									808.0
NYSPSC | CECONY | Steam
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA									190.0
Income tax benefit to be credited to customers resulting from TCJA									$ 15.0
Tax credit, amortization period									3 years
NYSPSC | CECONY | Scenario, Forecast | Electric
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA						$ 304.0				$ 247.0
NYSPSC | CECONY | Scenario, Forecast | Gas
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA						82.0				102.0
NYSPSC | CECONY | Scenario, Forecast | Steam
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA						6.0				$ 25.0
NYSPSC | CECONY | MTA Subway Power Outage
Public Utilities, General Disclosures [Line Items]
Regulatory costs		219.0						219.0	$ 219.0
Regulatory assets		189.0						189.0	189.0
NYSPSC | CECONY | MTA Subway Power Outage | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Regulatory costs						51.0
NYSPSC | CECONY | MTA Subway Power Outage | Electric
Public Utilities, General Disclosures [Line Items]
Regulatory costs		$ 30.0						$ 30.0	$ 30.0
NYSPSC | O&R | Scenario, Forecast | Electric and Gas
Public Utilities, General Disclosures [Line Items]
Income tax benefit to be credited to customers resulting from TCJA						$ 22.0
Tax credit, amortization period						3 years
NJBPU | RECO | Electric
Public Utilities, General Disclosures [Line Items]
Approved interim rate decrease	$ 2.9
Net benefit of the TCJA							$ 1.0
FERC | RECO
Public Utilities, General Disclosures [Line Items]
Impact in regulatory liability resulting from TCJA				$ 28.0
Impact in regulatory liability resulting from TCJA, subject to normalization requirements				$ 16.0