Regulatory Matters - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2016
Public Utilities, General Disclosures [Line Items]
Expected credit to customers				$ 116,000,000
Return on capital expenditures, not recoverable (up to)				55,000,000
Regulatory liabilities		$ 1,977,000,000		1,920,000,000
Prudence proceeding
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities		99,000,000		96,000,000
CECONY
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities		1,789,000,000		1,725,000,000
Requested deferral of incremental costs incurred to regulatory asset		35,000,000	$ 29,000,000
CECONY | Prudence proceeding
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities		$ 99,000,000		96,000,000
CECONY | June 2014 Plastic Fusion Proceeding
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities				$ 28,000,000
Scenario, Forecast | CECONY
Public Utilities, General Disclosures [Line Items]
Requested deferral of incremental costs incurred to regulatory asset	$ 37,000,000