Financial Information by Business Segment - Financial Data for the Business Segments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 955	$ 884	$ 840
Operating income	2,339	2,239	2,120
INCOME TAX EXPENSE	600	600	548
CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,176	8,228	8,376
Inter-segment revenues	15	12	12
Depreciation and amortization	710	656	623
Operating income	1,693	1,695	1,549
Interest charges	423	414	424
INCOME TAX EXPENSE	393	481	371
Total assets	28,339	27,123	25,045
Construction expenditures	1,375	1,354	1,421
CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,415	1,521	1,541
Inter-segment revenues	5	5	5
Depreciation and amortization	120	110	102
Operating income	346	295	310
Interest charges	82	78	82
INCOME TAX EXPENSE	99	43	91
Total assets	5,925	5,518	5,095
Construction expenditures	426	335	334
CECONY - Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	596	683	656
Inter-segment revenues	77	79	74
Depreciation and amortization	64	63	62
Operating income	54	93	63
Interest charges	40	42	43
INCOME TAX EXPENSE	22	43	29
Total assets	2,621	2,577	2,465
Construction expenditures	108	89	111
O&R - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	592	641	692
Inter-segment revenues
Depreciation and amortization	38	35	32
Operating income	83	81	74
Interest charges	19	20	22
INCOME TAX EXPENSE	17	21	18
Total assets	1,960	1,755	1,630
Construction expenditures	98	79	99
O&R - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	203	214	218
Inter-segment revenues
Depreciation and amortization	15	13	12
Operating income	40	33	34
Interest charges	10	12	12
INCOME TAX EXPENSE	11	9	8
Total assets	706	722	686
Construction expenditures	39	32	36
O&R - Other [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues
Depreciation and amortization
Operating income
Interest charges	2	2	1
Total assets	5	8	32
Competitive energy businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,213	1,617	1,883
Inter-segment revenues	8	13	9
Depreciation and amortization	8	7	9
Operating income	125	46	97
Interest charges	1	(1)	(3)
INCOME TAX EXPENSE	52	20	37
Total assets	1,061	856	828
Construction expenditures	492	114	28
Other Revenues And Eliminations In Segment Information [Member]
Segment Reporting Information [Line Items]
Operating revenues	(7)	(18)	(41)
Inter-segment revenues	(8)	(13)	(9)
Depreciation and amortization
Operating income	(2)	(4)	(7)
Interest charges	27	27	28
Total assets	592	655	567
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,187	10,432	10,573
Inter-segment revenues
Depreciation and amortization	894	829	787
Operating income	2,093	2,083	1,922
Interest charges	545	534	549
INCOME TAX EXPENSE	529	558	495
Total assets	36,885	35,218	32,605
Construction expenditures	1,909	1,778	1,866
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	795	855	910
Inter-segment revenues
Depreciation and amortization	53	48	44
Operating income	123	114	108
Interest charges	31	34	35
INCOME TAX EXPENSE	28	30	26
Total assets	2,671	2,485	2,348
Construction expenditures	137	111	135
Consolidation adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues	(97)	(96)	(91)
Depreciation and amortization
Operating income
Con Edison [Member]
Segment Reporting Information [Line Items]
Operating revenues	12,188	12,886	13,325
Inter-segment revenues
Depreciation and amortization	955	884	840
Operating income	2,339	2,239	2,120
Interest charges	604	594	609
INCOME TAX EXPENSE	594	617	554
Total assets	41,209	39,214	36,348
Construction expenditures	$ 2,538	$ 2,003	$ 2,029