Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 12,354	$ 12,188	$ 12,886
Inter-segment revenues
Depreciation and amortization	1,024	955	884
Operating income	2,244	2,339	2,239
Interest charges	719	604	594
INCOME TAX EXPENSE	504	594	617
Total assets	40,647	41,209	39,214
Construction expenditures	2,648	2,538	2,003
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,096	1,213	1,617
Inter-segment revenues	5	8	13
Depreciation and amortization	23	8	7
Operating income	63	125	46
Interest charges	135	1	(1)
INCOME TAX EXPENSE	(41)	52	20
Total assets	1,314	1,061	856
Construction expenditures	378	492	114
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(5)	(7)	(18)
Inter-segment revenues	(5)	(8)	(13)
Depreciation and amortization	(1)
Operating income	1	(2)	(4)
Interest charges	26	27	27
INCOME TAX EXPENSE	(6)
Total assets	530	592	655
Construction expenditures
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,430	10,187	10,432
Inter-segment revenues
Depreciation and amortization	946	894	829
Operating income	2,060	2,093	2,083
Interest charges	521	545	534
INCOME TAX EXPENSE	531	514	567
Total assets	36,258	36,885	35,218
Construction expenditures	2,135	1,909	1,778
CECONY [Member] | Operating Segments [Member] | CECONY-Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,131	8,176	8,228
Inter-segment revenues	16	15	12
Depreciation and amortization	749	710	656
Operating income	1,595	1,693	1,695
Interest charges	402	423	414
INCOME TAX EXPENSE	380	393	481
Total assets	27,673	28,339	27,123
Construction expenditures	1,471	1,375	1,354
CECONY [Member] | Operating Segments [Member] | CECONY-Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,616	1,415	1,521
Inter-segment revenues	5	5	5
Depreciation and amortization	130	120	110
Operating income	362	346	295
Interest charges	83	82	78
INCOME TAX EXPENSE	112	99	43
Total assets	6,008	5,925	5,518
Construction expenditures	536	426	335
CECONY [Member] | Operating Segments [Member] | CECONY-Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	683	596	683
Inter-segment revenues	82	77	79
Depreciation and amortization	67	64	63
Operating income	103	54	93
Interest charges	36	40	42
INCOME TAX EXPENSE	39	22	43
Total assets	2,577	2,621	2,577
Construction expenditures	128	108	89
CECONY [Member] | Consolidation Adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues	(103)	(97)	(96)
Depreciation and amortization
Operating income
Interest charges
INCOME TAX EXPENSE
Total assets
Construction expenditures
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	833	795	855
Inter-segment revenues
Depreciation and amortization	56	53	48
Operating income	120	123	114
Interest charges	37	31	34
INCOME TAX EXPENSE	20	28	30
Total assets	2,545	2,671	2,485
Construction expenditures	135	137	111
O&R [Member] | Operating Segments [Member] | O&R-Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	628	592	641
Inter-segment revenues
Depreciation and amortization	41	38	35
Operating income	87	83	81
Interest charges	25	19	20
INCOME TAX EXPENSE	13	17	21
Total assets	1,898	1,960	1,755
Construction expenditures	98	98	79
O&R [Member] | Operating Segments [Member] | O&R - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	205	203	214
Inter-segment revenues
Depreciation and amortization	15	15	13
Operating income	33	40	33
Interest charges	11	10	12
INCOME TAX EXPENSE	7	11	9
Total assets	645	706	722
Construction expenditures	37	39	32
O&R [Member] | Operating Segments [Member] | O&R - Other [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues
Depreciation and amortization
Operating income
Interest charges	1	2	2
INCOME TAX EXPENSE
Total assets	2	5	8
Construction expenditures