Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Gas) (Detail) (USD $)	12 Months Ended						36 Months Ended	12 Months Ended		36 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Cost reconciliation, deferred net regulatory assets	$ 615,000,000	$ 604,000,000
Cost reconciliations, deferred net regulatory liabilities	910,000,000	871,000,000
CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Cost reconciliation, deferred net regulatory assets	574,000,000	569,000,000
Cost reconciliations, deferred net regulatory liabilities	863,000,000	825,000,000
CECONY [Member] | Gas [Member]
Public Utilities, General Disclosures [Line Items]
Base rate changes	(54,600,000)		47,000,000		48,000,000	47,000,000
Amortizations to income of net regulatory (assets) and liabilities							(53,100,000)
Percentage of revenue reserve	15.00%		25.00%		25.00%	25.00%
Amount of revenues retained	70,000,000	64,000,000		57,000,000
Deferred revenues	28,000,000	36,000,000		22,000,000
Recognize penalties	0
Cost reconciliation, deferred net regulatory assets	38,000,000	26,000,000		9,000,000
Cost reconciliations, deferred net regulatory liabilities	0	9,500,000		2,900,000
Average rate base	3,521,000,000		3,434,000,000		3,245,000,000	3,027,000,000
Authorized return on common equity, austerity measures		2,000,000		4,000,000
Weighted average cost of capital (after-tax)	7.10%		7.46%		7.46%	7.46%
Authorized return on common equity	9.30%		9.60%		9.60%	9.60%
Earnings sharing percentage	9.90%		10.15%		10.15%	10.35%	10.15%
Cost of long-term debt	5.17%		5.57%		5.57%	5.57%	5.57%
Common equity ratio	48.00%		48.00%		48.00%	48.00%
Negative revenue adjustments		0		0
CECONY [Member] | Gas [Member] | Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
Base rate changes								56,800,000	38,600,000
Amortizations to income of net regulatory (assets) and liabilities										4,000,000
Percentage of revenue reserve								15.00%	15.00%
Average rate base								4,236,000,000	3,863,000,000
Weighted average cost of capital (after-tax)								7.21%	7.13%
Authorized return on common equity								9.30%	9.30%
Earnings sharing percentage								9.90%	9.90%	9.90%
Cost of long-term debt								5.39%	5.23%	5.39%
Common equity ratio								48.00%	48.00%
CECONY [Member] | Gas [Member] | Gas Delivery [Member]
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations	3,899,000,000		3,346,000,000		3,148,000,000	2,934,000,000
CECONY [Member] | Gas [Member] | Gas Delivery [Member] | Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								4,698,000,000	4,258,000,000
CECONY [Member] | Gas [Member] | Storm Hardening [Member]
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations	3,000,000
CECONY [Member] | Gas [Member] | Storm Hardening [Member] | Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								30,000,000	8,000,000
CECONY [Member] | Maximum [Member] | Gas [Member]
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained	65,000,000		58,000,000		58,000,000	58,000,000	58,000,000
Potential penalties	33,000,000		12,600,000		12,600,000	12,600,000
CECONY [Member] | Maximum [Member] | Gas [Member] | Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained								65,000,000	65,000,000	65,000,000
Potential penalties								$ 56,000,000	$ 44,000,000