Financial Information by Business Segment - Financial Data for Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 3,417	$ 3,443	$ 9,368	$ 9,847
Depreciation and amortization	305	285	905	840
Operating income	940	830	2,097	2,028
Other income (deductions)	49	9	61	23
Interest charges	178	162	517	486
Income taxes on operating income	321	260	620	574
Total assets	47,316	44,971	47,316	44,971	$ 45,642
Construction expenditures	818	874	2,579	2,473
CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,828	2,829	7,741	8,122
Depreciation and amortization	278	262	825	773
Operating income	766	745	1,799	1,889
Other income (deductions)	2	(3)	2	(4)
Interest charges	154	145	451	435
Income taxes on operating income	234	225	503	525
Total assets	40,436	39,670	40,436	39,670	$ 40,230
Construction expenditures	659	624	1,796	1,696
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	217	207	645	610
Operating income	841	811	1,487	1,511
Other income (deductions)	2	(2)	3	(3)
Interest charges	117	111	342	333
Income taxes on operating income	275	260	412	401
Total assets	30,580	30,369	30,580	30,369
Construction expenditures	411	419	1,133	1,165
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	41	35	118	105
Operating income	(28)	(17)	273	278
Other income (deductions)	0	(1)	(1)	(1)
Interest charges	27	24	79	71
Income taxes on operating income	(24)	(17)	73	82
Total assets	7,300	6,687	7,300	6,687
Construction expenditures	224	178	589	466
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	20	20	62	58
Operating income	(47)	(49)	39	100
Other income (deductions)	0	0	0	0
Interest charges	10	10	30	31
Income taxes on operating income	(17)	(18)	18	42
Total assets	2,556	2,614	2,556	2,614
Construction expenditures	24	27	74	65
O&R
Segment Reporting Information [Line Items]
Depreciation and amortization	17	17	50	51
Operating income	48	42	114	85
Other income (deductions)	1	(5)	1	(4)
Interest charges	9	9	28	27
Income taxes on operating income	16	12	35	22
Total assets	2,784	2,713	2,784	2,713
Construction expenditures	38	38	106	101
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	12	13	37	38
Operating income	55	51	86	85
Other income (deductions)	1	(4)	1	(2)
Interest charges	6	6	19	18
Income taxes on operating income	20	17	27	26
Total assets	1,985	1,959	1,985	1,959
Construction expenditures	24	26	70	72
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	5	4	13	13
Operating income	(7)	(9)	28	0
Other income (deductions)	0	(1)	0	(2)
Interest charges	3	3	9	9
Income taxes on operating income	(4)	(5)	8	(4)
Total assets	799	754	799	754
Construction expenditures	14	12	36	29
Competitive energy businesses
Segment Reporting Information [Line Items]
Depreciation and amortization	11	6	30	16
Operating income	125	43	184	53
Other income (deductions)	27	17	36	33
Interest charges	7	2	23	5
Income taxes on operating income	67	21	76	24
Total assets	2,394	1,547	2,394	1,547
Construction expenditures	121	212	677	676
Con Edison Transmission
Segment Reporting Information [Line Items]
Operating income	(1)	0	(1)	0
Other income (deductions)	20	0	23	0
Interest charges	3	0	4	0
Income taxes on operating income	0	0	0	0
Total assets	1,072	2	1,072	2
Construction expenditures	0	0	0	0
Other
Segment Reporting Information [Line Items]
Depreciation and amortization	(1)	0	0	0
Operating income	2	0	1	1
Other income (deductions)	(1)	0	(1)	(2)
Interest charges	5	6	11	19
Income taxes on operating income	4	2	6	3
Total assets	630	1,039	630	1,039
Construction expenditures	0	0	0	0
Operating revenues
Segment Reporting Information [Line Items]
Operating revenues	3,417	3,443	9,368	9,847
Operating revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,828	2,829	7,741	8,122
Operating revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	2,557	2,558	6,222	6,416
Operating revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	208	213	1,113	1,177
Operating revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	63	58	406	529
Operating revenues | O&R
Segment Reporting Information [Line Items]
Operating revenues	240	229	630	640
Operating revenues | O&R | Electric
Segment Reporting Information [Line Items]
Operating revenues	213	205	497	523
Operating revenues | O&R | Gas
Segment Reporting Information [Line Items]
Operating revenues	27	24	133	117
Operating revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	350	386	998	1,087
Operating revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	(1)	(1)	(1)	(2)
Inter-segment revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	(28)	(27)	(82)	(82)
Inter-segment revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	5	4	13	13
Inter-segment revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	1	1	4	4
Inter-segment revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	22	22	65	65
Inter-segment revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	(2)	(2)	7	(5)
Inter-segment revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	$ 2	$ 2	$ (7)	$ 5