Regulatory Matters - Regulatory Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory assets - long-term	$ 9,304	$ 9,705
Regulatory assets - current	56	74
Regulatory liabilities - long-term	1,393	1,202
Total Regulatory Assets	9,360	9,779
Regulatory liabilities - current	88	183
Total Regulatory Liabilities	1,481	1,385
Unrecognized pension and other postretirement costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	5,227	5,677
Future income tax [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	1,996	1,922
Environmental remediation costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	713	730
Deferred storm costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	454	432
Pension and other postretirement benefits deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	201	183
Revenue taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	183	176
Net electric deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	92	102
Unamortized loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	69	74
Surcharge for New York State assessment [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	55	73
Deferred derivative losses - long-term [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	41	40
O&R transition bond charges [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	36	39
Preferred stock redemption [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	29	29
Workers' compensation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	18	19
Property tax reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	18	16
Regulatory liabilities - long-term	273	187
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	172	193
Deferred derivative losses - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	55	69
Recoverable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	1	5
Allowance for cost removal less salvage [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	518	503
Net unbilled revenue deferrals [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	137	136
Long-term interest rate reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	83	62
World Trade Center settlement proceeds [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	62
Carrying charges on transmission and distribution net plant [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	26	31
Expenditure prudence proceeding [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	16	14
Other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	278	207
Refundable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	63	82
Revenue decoupling mechanism [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	23	72
Deferred derivative gains - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	2
Electric surcharge offset [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current		29
CECONY [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	8,595	8,972
Regulatory assets - current	51	60
Regulatory liabilities - long-term	1,269	1,077
Total Regulatory Assets	8,646	9,032
Regulatory liabilities - current	54	145
Total Regulatory Liabilities	1,323	1,222
CECONY [Member] | Unrecognized pension and other postretirement costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	4,985	5,407
CECONY [Member] | Future income tax [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	1,889	1,831
CECONY [Member] | Environmental remediation costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	599	615
CECONY [Member] | Deferred storm costs [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	336	309
CECONY [Member] | Pension and other postretirement benefits deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	170	154
CECONY [Member] | Revenue taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	176	170
CECONY [Member] | Net electric deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	92	102
CECONY [Member] | Unamortized loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	66	70
CECONY [Member] | Surcharge for New York State assessment [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	53	68
CECONY [Member] | Deferred derivative losses - long-term [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	20	20
CECONY [Member] | Preferred stock redemption [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	29	29
CECONY [Member] | Workers' compensation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	18	19
CECONY [Member] | Property tax reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	273	187
CECONY [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	162	178
CECONY [Member] | Deferred derivative losses - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	51	60
CECONY [Member] | Recoverable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current
CECONY [Member] | Allowance for cost removal less salvage [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	433	420
CECONY [Member] | Net unbilled revenue deferrals [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	137	136
CECONY [Member] | Long-term interest rate reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	83	62
CECONY [Member] | World Trade Center settlement proceeds [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	62	62
CECONY [Member] | Carrying charges on transmission and distribution net plant [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	14	13
CECONY [Member] | Expenditure prudence proceeding [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	16	14
CECONY [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	251	183
CECONY [Member] | Refundable energy costs - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	32	48
CECONY [Member] | Revenue decoupling mechanism [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	21	68
CECONY [Member] | Deferred derivative gains - current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	1
CECONY [Member] | Electric surcharge offset [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current		$ 29