Regulatory Matters - Summary of Rate Plan (Detail) - Jun. 30, 2015 - USD ($)	Total	Total
CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Potential refund from customers		$ 249,000,000
O&R | Electric
Public Utilities, General Disclosures [Line Items]
Potential penalties	$ 4,000,000
Deferred storm and property reserve deficiency	59,300,000	59,300,000
Deferred storm and property deficiency not recovered	1,000,000	1,000,000
Storm Reserve | CECONY
Public Utilities, General Disclosures [Line Items]
Revenue requirement	21,000,000	21,000,000
Deferred storm costs | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory asset		107,000,000
Reduction of costs recoverable from customers		4,000,000
Property Tax and Interest Rate Reconciliations | O&R | Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets not recoverable	4,000,000	4,000,000
Property Tax and Interest Rate Reconciliations | O&R | Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets not recoverable	14,000,000	$ 14,000,000
Year 1 | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Amortizations to income of net regulatory (assets) liabilities	123,000,000
Retention of annual transmission congestion revenues	90,000,000
Average rate base	$ 18,282,000,000
Weighted average cost of capital (after-tax) (percent)	6.91%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.09%	5.09%
Common equity ratio (percent)	48.00%
Year 1 | CECONY | Electric | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties	$ 400,000,000
Year 1 | O&R | Electric
Public Utilities, General Disclosures [Line Items]
Base rate changes	9,300,000	$ 9,300,000
Amortizations to income of net regulatory (assets) liabilities	(8,500,000)
Net utility plant reconciliations	928,000,000
Average rate base	$ 763,000,000
Weighted average cost of capital (after-tax) (percent)	7.10%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.42%	5.42%
Common equity ratio (percent)	48.00%
Deferred storm and property reserve deficiency	$ 11,850,000	$ 11,850,000
Rate exclusion amount with balance below regulatory threshold	1,000,000
Year 1 | O&R | Gas
Public Utilities, General Disclosures [Line Items]
Base rate changes	27,500,000	$ 27,500,000
Amortizations to income of net regulatory (assets) liabilities	(1,700,000)
Potential penalties	3,700,000.0
Net utility plant reconciliations	492,000,000
Average rate base	$ 366,000,000
Weighted average cost of capital (after-tax) (percent)	7.10%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.42%	5.42%
Common equity ratio (percent)	48.00%
Potential base rate changes	$ 16,400,000	$ 16,400,000
Rate exclusion amount with balance below regulatory threshold	500,000
Year 1 | T&D | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations	17,929,000,000
Year 1 | Storm Hardening | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations	268,000,000
Year 1 | Other | CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations	2,069,000,000
Year 2 | O&R | Electric
Public Utilities, General Disclosures [Line Items]
Base rate changes	8,800,000	$ 8,800,000
Amortizations to income of net regulatory (assets) liabilities	(9,400,000)
Net utility plant reconciliations	970,000,000
Average rate base	$ 805,000,000
Weighted average cost of capital (after-tax) (percent)	7.06%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.35%	5.35%
Common equity ratio (percent)	48.00%
Deferred storm and property reserve deficiency	$ 11,850,000	$ 11,850,000
Deferred storm and property reserve deficiency period (in years)	5 years
Rate exclusion amount with balance below regulatory threshold	$ 9,000,000
Year 2 | O&R | Gas
Public Utilities, General Disclosures [Line Items]
Base rate changes	4,400,000	$ 4,400,000
Amortizations to income of net regulatory (assets) liabilities	(2,100,000)
Potential penalties	4,700,000.0
Net utility plant reconciliations	518,000,000
Average rate base	$ 391,000,000
Weighted average cost of capital (after-tax) (percent)	7.06%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.35%	5.35%
Common equity ratio (percent)	48.00%
Potential base rate changes	$ 16,400,000	$ 16,400,000
Rate exclusion amount with balance below regulatory threshold	4,200,000
Year 3 | O&R | Gas
Public Utilities, General Disclosures [Line Items]
Base rate changes	6,700,000	$ 6,700,000
Amortizations to income of net regulatory (assets) liabilities	(2,500,000)
Potential penalties	5,800,000.0
Net utility plant reconciliations	546,000,000
Average rate base	$ 417,000,000
Weighted average cost of capital (after-tax) (percent)	7.06%
Authorized return on common equity (percent)	9.00%
Earnings sharing percentage	9.60%	9.60%
Cost of long-term debt (percent)	5.35%	5.35%
Common equity ratio (percent)	48.00%
Potential base rate changes	$ 5,800,000	$ 5,800,000
Potential base rate surcharge	10,600,000	$ 10,600,000
Rate exclusion amount with balance below regulatory threshold	$ 7,200,000