Financial Information by Business Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 12,033	$ 12,075	$ 12,554
Depreciation and amortization	1,341	1,216	1,130
Operating income	2,610	2,575	2,427
Other Income (deductions)	116	64	24
Interest charges	729	696	653
Income taxes on operating income	459	714	644
Total assets	48,111	48,255	45,642
Capital expenditures	3,606	5,235	3,418
Income taxes on non-operating income	$ 13	$ (16)	$ (40)
Corporate income tax rate	35.00%	35.00%	35.00%
Federal income tax expense	$ 259
Parent Company
Segment Reporting Information [Line Items]
Interest charges	50	$ 41	$ 29
Total assets	17,231	16,192
Federal income tax expense	(21)
Clean Energy Businesses
Segment Reporting Information [Line Items]
Federal income tax expense	269
Con Edison Transmission
Segment Reporting Information [Line Items]
Federal income tax expense	11
CECONY
Segment Reporting Information [Line Items]
Revenues	10,468	10,165	10,328
Depreciation and amortization	1,195	1,106	1,040
Operating income	2,405	2,262	2,247
Other Income (deductions)	7	0	(5)
Interest charges	623	603	584
Total assets	40,451	40,856
Income taxes on non-operating income	$ (3)	$ (14)	$ (14)
Corporate income tax rate	35.00%	35.00%	35.00%
Operating segment | Clean Energy Businesses
Segment Reporting Information [Line Items]
Revenues	$ 694	$ 1,091	$ 1,383
Depreciation and amortization	74	42	22
Operating income	69	183	58
Other Income (deductions)	33	21	35
Interest charges	43	34	11
Income taxes on operating income	(273)	53	22
Total assets	2,735	2,551	1,680
Capital expenditures	447	1,235	823
Operating segment | Con Edison Transmission
Segment Reporting Information [Line Items]
Revenues	2	0	0
Depreciation and amortization	1	0	0
Operating income	(8)	(3)	0
Other Income (deductions)	80	43	0
Interest charges	16	6	0
Income taxes on operating income	(11)	0	0
Total assets	1,222	1,150	3
Capital expenditures	66	1,078	0
Operating segment | CECONY
Segment Reporting Information [Line Items]
Revenues	10,468	10,165	10,328
Depreciation and amortization	1,195	1,106	1,040
Operating income	2,405	2,262	2,247
Other Income (deductions)	7	0	(5)
Interest charges	623	603	584
Income taxes on operating income	688	617	588
Total assets	40,451	40,856	40,230
Capital expenditures	2,904	2,756	2,435
Operating segment | CECONY | Electric
Segment Reporting Information [Line Items]
Revenues	7,972	8,106	8,172
Depreciation and amortization	925	865	820
Operating income	1,862	1,847	1,798
Other Income (deductions)	7	2	(2)
Interest charges	472	459	447
Income taxes on operating income	511	495	447
Total assets	29,661	30,708	30,603
Capital expenditures	1,905	1,819	1,658
Operating segment | CECONY | Gas
Segment Reporting Information [Line Items]
Revenues	1,901	1,508	1,527
Depreciation and amortization	185	159	142
Operating income	472	357	356
Other Income (deductions)	0	(1)	(2)
Interest charges	113	105	96
Income taxes on operating income	152	92	100
Total assets	8,387	7,553	6,974
Capital expenditures	909	811	671
Operating segment | CECONY | Steam
Segment Reporting Information [Line Items]
Revenues	595	551	629
Depreciation and amortization	85	82	78
Operating income	71	58	93
Other Income (deductions)	0	(1)	(1)
Interest charges	38	39	41
Income taxes on operating income	25	30	41
Total assets	2,403	2,595	2,653
Capital expenditures	90	126	106
Operating segment | O&R
Segment Reporting Information [Line Items]
Revenues	874	821	845
Depreciation and amortization	71	67	68
Operating income	141	130	121
Other Income (deductions)	1	1	(4)
Interest charges	36	36	35
Income taxes on operating income	42	40	33
Total assets	2,773	2,758	2,719
Capital expenditures	189	166	160
Operating segment | O&R | Electric
Segment Reporting Information [Line Items]
Revenues	642	637	663
Depreciation and amortization	51	49	50
Operating income	100	95	103
Other Income (deductions)	1	1	(2)
Interest charges	24	24	23
Income taxes on operating income	30	30	31
Total assets	1,949	1,949	2,140
Capital expenditures	128	114	114
Operating segment | O&R | Gas
Segment Reporting Information [Line Items]
Revenues	232	184	182
Depreciation and amortization	20	18	18
Operating income	41	35	18
Other Income (deductions)	0	0	(2)
Interest charges	12	12	12
Income taxes on operating income	12	10	2
Total assets	824	809	579
Capital expenditures	61	52	46
Other
Segment Reporting Information [Line Items]
Revenues	(5)	(2)	(2)
Depreciation and amortization	0	1	0
Operating income	3	3	1
Other Income (deductions)	(5)	(1)	(2)
Interest charges	11	17	23
Income taxes on operating income	13	4	1
Total assets	930	940	1,010
Capital expenditures	0	0	0
Other | O&R
Segment Reporting Information [Line Items]
Revenues	0	0	0
Depreciation and amortization	0	0	0
Operating income	0	0	0
Other Income (deductions)	0	0	0
Interest charges	0	0	0
Income taxes on operating income	0	0	0
Total assets	0	0	0
Capital expenditures	0	0	0
Inter-segment
Segment Reporting Information [Line Items]
Revenues	0	(7)	2
Inter-segment | Clean Energy Businesses
Segment Reporting Information [Line Items]
Revenues	0	7	(2)
Inter-segment | CECONY
Segment Reporting Information [Line Items]
Revenues	(97)	(111)	(110)
Inter-segment | CECONY | Electric
Segment Reporting Information [Line Items]
Revenues	16	17	18
Inter-segment | CECONY | Gas
Segment Reporting Information [Line Items]
Revenues	6	6	6
Inter-segment | CECONY | Steam
Segment Reporting Information [Line Items]
Revenues	$ 75	$ 88	$ 86