Financial Information by Business Segment - Financial Data for Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 2,794	$ 2,788	$ 5,950	$ 6,404
Depreciation and amortization	302	276	599	555
Operating income	515	472	1,157	1,198
Other income (deductions)	11	10	12	14
Interest charges	170	162	339	323
Income taxes on operating income	128	108	299	314
Total assets	47,270	44,751	47,270	44,751	$ 45,642
Construction expenditures	736	991	1,760	1,597
CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,281	2,283	4,913	5,292
Depreciation and amortization	275	254	547	511
Operating income	392	460	1,033	1,143
Other income (deductions)	2	(2)	0	(1)
Interest charges	149	146	297	290
Income taxes on operating income	87	105	269	300
Total assets	40,353	39,701	40,353	39,701	$ 40,230
Construction expenditures	571	591	1,136	1,071
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	215	201	428	403
Operating income	371	422	645	700
Other income (deductions)	2	(1)	1	(1)
Interest charges	113	113	225	223
Income taxes on operating income	88	99	137	142
Total assets	30,632	30,474	30,632	30,474
Construction expenditures	338	409	720	744
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	39	35	78	70
Operating income	48	54	301	294
Other income (deductions)	0	(1)	(1)	0
Interest charges	26	23	52	46
Income taxes on operating income	9	12	97	98
Total assets	7,131	6,598	7,131	6,598
Construction expenditures	205	161	365	289
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	21	18	41	38
Operating income	(27)	(16)	87	149
Other income (deductions)	0	0	0	0
Interest charges	10	10	20	21
Income taxes on operating income	(10)	(6)	35	60
Total assets	2,590	2,629	2,590	2,629
Construction expenditures	28	21	51	38
O&R
Segment Reporting Information [Line Items]
Depreciation and amortization	17	17	33	34
Operating income	13	(2)	66	43
Other income (deductions)	0	0	0	1
Interest charges	9	9	18	17
Income taxes on operating income	2	(4)	19	10
Total assets	2,689	2,683	2,689	2,683
Construction expenditures	37	36	68	62
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	13	13	24	25
Operating income	14	16	32	34
Other income (deductions)	0	0	0	1
Interest charges	6	5	12	11
Income taxes on operating income	3	4	7	9
Total assets	1,928	1,944	1,928	1,944
Construction expenditures	25	25	47	45
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	9	9
Operating income	(1)	(18)	34	9
Other income (deductions)	0	0	0	0
Interest charges	3	4	6	6
Income taxes on operating income	(1)	(8)	12	1
Total assets	761	739	761	739
Construction expenditures	12	11	21	17
Competitive energy businesses
Segment Reporting Information [Line Items]
Depreciation and amortization	10	6	19	11
Operating income	109	13	58	10
Other income (deductions)	7	12	9	15
Interest charges	8	2	16	3
Income taxes on operating income	36	7	9	4
Total assets	2,494	1,549	2,494	1,549
Construction expenditures	128	364	556	464
Con Edison Transmission
Segment Reporting Information [Line Items]
Operating income	(1)	0	(1)	0
Other income (deductions)	3	0	3	0
Interest charges	1	0	1	0
Income taxes on operating income	0	0	0	0
Total assets	1,043	2	1,043	2
Construction expenditures	0	0	0	0
Other
Segment Reporting Information [Line Items]
Depreciation and amortization	0	(1)	0	(1)
Operating income	2	1	1	2
Other income (deductions)	(1)	0	0	(1)
Interest charges	3	5	7	13
Income taxes on operating income	3	0	2	0
Total assets	691	816	691	816
Construction expenditures	0	0	0	0
Operating revenues
Segment Reporting Information [Line Items]
Operating revenues	2,794	2,788	5,950	6,404
Operating revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,281	2,283	4,913	5,292
Operating revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	1,892	1,879	3,665	3,858
Operating revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	304	308	905	963
Operating revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	85	96	343	471
Operating revenues | O&R
Segment Reporting Information [Line Items]
Operating revenues	175	178	390	411
Operating revenues | O&R | Electric
Segment Reporting Information [Line Items]
Operating revenues	144	162	284	318
Operating revenues | O&R | Gas
Segment Reporting Information [Line Items]
Operating revenues	31	16	106	93
Operating revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	338	328	648	702
Operating revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	0	(1)	(1)	(1)
Inter-segment revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	(26)	(27)	(56)	(55)
Inter-segment revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	4	5	9	9
Inter-segment revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	1	1	3	3
Inter-segment revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	21	21	44	43
Inter-segment revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	3	(1)	9	(4)
Inter-segment revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	$ (3)	$ 1	$ (9)	$ 4