Regulatory Matters - Summary of Rate Plan (Detail) - CECONY $ in Millions	1 Months Ended
	Mar. 31, 2016 USD ($)
Year 1 | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	$ 2
Public utilities, requested rate increase (decrease), amount	480
Year 1 | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	5
Public utilities, requested rate increase (decrease), amount	159
Year 2 | Electric
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	3
Public utilities, requested rate increase (decrease), amount	177
Year 2 | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	(4)
Public utilities, requested rate increase (decrease), amount	93
Year 3 | Electric
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	141
Year 3 | Gas
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in requested rate amount	(5)
Public utilities, requested rate increase (decrease), amount	$ 104