Regulatory Matters - Summary of Rate Plan (Detail) - USD ($) $ in Millions	1 Months Ended				6 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Jun. 30, 2016
Year 1 | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		$ 16
Public utilities, requested rate increase (decrease), amount		498
Year 1 | CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		(29)
Public utilities, requested rate increase (decrease), amount		125
Year 2 | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		(11)
Public utilities, requested rate increase (decrease), amount		169
Year 2 | CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		13
Public utilities, requested rate increase (decrease), amount		110
Year 3 | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		45
Public utilities, requested rate increase (decrease), amount		186
Year 3 | CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount		9
Public utilities, requested rate increase (decrease), amount		$ 100
NYSPSC | NYSPSC January 2016 Proceeding | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Return on common equity (percent)					9.75%
NYSPSC | NYSPSC January 2016 Proceeding | Year 1 | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount			$ 45
Return on common equity (percent)			8.60%
NYSPSC | NYSPSC January 2016 Proceeding | Year 1 | CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount			$ (25)
Return on common equity (percent)			8.60%
New Jersey Board of Public Utilities | Rockland Electric Company | Year 1 | Rockland Electric Company | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount				$ 10
Return on common equity (percent)				10.20%
Common equity ratio (percent)				49.81%
New Jersey Board of Public Utilities | Rockland Electric Company | Subsequent Event | Year 1 | Rockland Electric Company | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	$ (1)
Return on common equity (percent)	10.20%
Common equity ratio (percent)	49.71%
New Jersey Board of Public Utilities | Rockland Electric Company | Subsequent Event | Year 2 | Rockland Electric Company | Electric
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 9