Regulatory Matters - Regulatory Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
Regulatory assets - long-term	$ 9,705	$ 9,431
Regulatory assets - current	74	164
Regulatory liabilities - long-term	1,202	977
Total Regulatory Assets	9,779	9,595
Regulatory liabilities - current	183	118
Total Regulatory Liabilities	1,385	1,095
Unrecognized pension and other postretirement costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	5,677	5,852
Future income tax [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	1,922	1,798
Environmental remediation costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	730	681
Deferred storm costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	432	128
Pension and other post retirement benefits deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	183	198
Revenue taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	176	163
Net electric deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	102	121
Unamortized loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	74	84
Surcharge for New York State assessment [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	73	90
Deferred derivative losses - long-term [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	40	60
O&R transition bond charges [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	39	44
Preferred Stock Redemption [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	29
Recoverable energy costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	23	14
Regulatory assets - current	5
Workers' compensation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	19	23
Property tax reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	16	13
Regulatory liabilities - long-term	187	35
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	170	162
Deferred derivative losses - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	69	164
Allowance for cost removal less salvage [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	503	448
Net unbilled revenue deferrals [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	136	104
Regulatory liabilities - current	136
World Trade Center settlement proceeds [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	62
Long-term interest rate reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	30
Carrying charges on transmission and distribution net plant [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	31	38
Gas line losses [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	14	21
Expenditure prudence proceeding [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	14	11
Energy efficiency programs [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	5	22
Other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	188	206
Refundable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	82	51
Revenue decoupling mechanism [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	72	66
Electric Surcharge Offset [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	29
Deferred derivative gains - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current		1
CECONY [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	8,972	8,750
Regulatory assets - current	60	140
Regulatory liabilities - long-term	1,077	861
Total Regulatory Assets	9,032	8,890
Regulatory liabilities - current	145	79
Total Regulatory Liabilities	1,222	940
CECONY [Member] | Unrecognized pension and other postretirement costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	5,407	5,554
CECONY [Member] | Future income tax [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	1,831	1,724
CECONY [Member] | Environmental remediation costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	615	564
CECONY [Member] | Deferred storm costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	309	80
CECONY [Member] | Pension and other post retirement benefits deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	154	157
CECONY [Member] | Revenue taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	170	158
CECONY [Member] | Net electric deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	102	121
CECONY [Member] | Unamortized loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	70	80
CECONY [Member] | Surcharge for New York State assessment [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	68	82
CECONY [Member] | Deferred derivative losses - long-term [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	20	44
CECONY [Member] | Preferred Stock Redemption [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	29
CECONY [Member] | Recoverable energy costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	23	14
CECONY [Member] | Workers' compensation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	19	23
CECONY [Member] | Property tax reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	187	35
CECONY [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	155	149
CECONY [Member] | Deferred derivative losses - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	60	140
CECONY [Member] | Allowance for cost removal less salvage [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	420	372
CECONY [Member] | Net unbilled revenue deferrals [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	136	104
CECONY [Member] | World Trade Center settlement proceeds [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	62
CECONY [Member] | Long-term interest rate reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	30
CECONY [Member] | Carrying charges on transmission and distribution net plant [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	13	14
CECONY [Member] | Gas line losses [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	14	21
CECONY [Member] | Expenditure prudence proceeding [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	14	11
CECONY [Member] | Energy efficiency programs [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	6	20
CECONY [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	163	192
CECONY [Member] | Refundable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	48	12
CECONY [Member] | Revenue decoupling mechanism [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	68	66
CECONY [Member] | Electric Surcharge Offset [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	29
CECONY [Member] | Deferred derivative gains - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current		$ 1