Regulatory Matters - Regulatory Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Regulatory assets
Regulatory assets - long-term	$ 7,082	$ 7,201
Regulatory assets - current	8	29
Total Regulatory Assets	7,090	7,230
Regulatory liabilities
Regulatory liabilities - noncurrent	1,800	1,728
Regulatory liabilities - current	243	148
Total Regulatory Liabilities	2,043	1,876
Allowance for Cost Removal Less Salvage [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	558	540
Property Tax Refunds [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	119	130
Long-Term Interest Rate Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	99	105
Net Unbilled Revenue Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	61	133
Other Postretirement Benefit Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	51	50
Carrying Charges on Repair Allowance and Bonus Depreciation [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	81	88
New York State Income Tax Rate Change [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	66
World Trade Center Settlement Proceeds [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	57	62
2014 Rate Plan Base Rate Revenue Deferral [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	50
Prudence Proceeding [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	38	40
Unrecognized Other Postretirement Benefits Costs [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	32
Carrying Charges on Transmission and Distribution Net Plant [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	27	28
Electric Excess Earnings [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	22	22
Other [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	240	208
Refundable Energy Costs - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	160	100
Deferred Derivative Gains - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	44	14
Revenue Decoupling Mechanism [Member]
Regulatory liabilities
Regulatory liabilities - current	23	34
Future Income Tax [Member]
Regulatory liabilities
Regulatory liabilities - current	16
Unrecognized Pension and Other Postretirement Costs [Member]
Regulatory assets
Regulatory assets - long-term	2,591	2,730
Future Income Tax [Member]
Regulatory assets
Regulatory assets - long-term	2,183	2,145
Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - long-term	921	938
Deferred Storm Costs [Member]
Regulatory assets
Regulatory assets - long-term	411	441
Revenue Taxes [Member]
Regulatory assets
Regulatory assets - long-term	216	207
Pension and Other Postretirement Benefits Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	191	237
Surcharge for New York State Assessment [Member]
Regulatory assets
Regulatory assets - long-term	144	78
Net Electric Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	78	83
Unamortized Loss on Reacquired Debt [Member]
Regulatory assets
Regulatory assets - long-term	63	65
O&R Transition Bond Charges [Member]
Regulatory assets
Regulatory assets - long-term	31	33
Preferred Stock Redemption [Member]
Regulatory assets
Regulatory assets - long-term	28	28
Property Tax Reconciliation [Member]
Regulatory assets
Regulatory assets - long-term	25	22
Regulatory liabilities
Regulatory liabilities - noncurrent	299	322
Workers' Compensation [Member]
Regulatory assets
Regulatory assets - long-term	12	12
Deferred Derivative Losses - Noncurrent [Member]
Regulatory assets
Regulatory assets - long-term	6	8
Other [Member]
Regulatory assets
Regulatory assets - long-term	182	174
Deferred Derivative Losses - Current [Member]
Regulatory assets
Regulatory assets - current	7	25
Recoverable Energy Costs - Current [Member]
Regulatory assets
Regulatory assets - current	1	4
CECONY [Member]
Regulatory assets
Regulatory assets - long-term	6,522	6,639
Regulatory assets - current	5	26
Total Regulatory Assets	6,527	6,665
Regulatory liabilities
Regulatory liabilities - noncurrent	1,647	1,598
Regulatory liabilities - current	199	107
Total Regulatory Liabilities	1,846	1,705
CECONY [Member] | Allowance for Cost Removal Less Salvage [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	466	453
CECONY [Member] | Property Tax Refunds [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	119	130
CECONY [Member] | Long-Term Interest Rate Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	99	105
CECONY [Member] | Net Unbilled Revenue Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	61	133
CECONY [Member] | Other Postretirement Benefit Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	47	50
CECONY [Member] | Carrying Charges on Repair Allowance and Bonus Depreciation [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	80	87
CECONY [Member] | New York State Income Tax Rate Change [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	62
CECONY [Member] | World Trade Center Settlement Proceeds [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	57	62
CECONY [Member] | 2014 Rate Plan Base Rate Revenue Deferral [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	50
CECONY [Member] | Prudence Proceeding [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	38	40
CECONY [Member] | Unrecognized Other Postretirement Benefits Costs [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	23
CECONY [Member] | Carrying Charges on Transmission and Distribution Net Plant [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	21	20
CECONY [Member] | Electric Excess Earnings [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	18	18
CECONY [Member] | Other [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	207	178
CECONY [Member] | Refundable Energy Costs - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	128	66
CECONY [Member] | Deferred Derivative Gains - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	36	11
CECONY [Member] | Revenue Decoupling Mechanism [Member]
Regulatory liabilities
Regulatory liabilities - current	19	30
CECONY [Member] | Future Income Tax [Member]
Regulatory liabilities
Regulatory liabilities - current	16
CECONY [Member] | Unrecognized Pension and Other Postretirement Costs [Member]
Regulatory assets
Regulatory assets - long-term	2,478	2,610
CECONY [Member] | Future Income Tax [Member]
Regulatory assets
Regulatory assets - long-term	2,070	2,030
CECONY [Member] | Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - long-term	814	830
CECONY [Member] | Deferred Storm Costs [Member]
Regulatory assets
Regulatory assets - long-term	307	334
CECONY [Member] | Revenue Taxes [Member]
Regulatory assets
Regulatory assets - long-term	204	196
CECONY [Member] | Pension and Other Postretirement Benefits Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	163	211
CECONY [Member] | Surcharge for New York State Assessment [Member]
Regulatory assets
Regulatory assets - long-term	136	74
CECONY [Member] | Net Electric Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	78	83
CECONY [Member] | Unamortized Loss on Reacquired Debt [Member]
Regulatory assets
Regulatory assets - long-term	60	62
CECONY [Member] | Preferred Stock Redemption [Member]
Regulatory assets
Regulatory assets - long-term	28	28
CECONY [Member] | Property Tax Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	299	322
CECONY [Member] | Workers' Compensation [Member]
Regulatory assets
Regulatory assets - long-term	12	12
CECONY [Member] | Deferred Derivative Losses - Noncurrent [Member]
Regulatory assets
Regulatory assets - long-term	5	7
CECONY [Member] | Other [Member]
Regulatory assets
Regulatory assets - long-term	167	162
CECONY [Member] | Deferred Derivative Losses - Current [Member]
Regulatory assets
Regulatory assets - current	5	22
CECONY [Member] | Recoverable Energy Costs - Current [Member]
Regulatory assets
Regulatory assets - current		$ 4