Financial Information by Business Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 3,211	$ 3,417	$ 9,072	$ 9,368
Depreciation and amortization	337	305	998	905
Operating income/(loss)	873	940	2,066	2,097
Clean Energy Businesses
Segment Reporting Information [Line Items]
Depreciation and amortization	19	11	54	30
Operating income/(loss)	29	125	63	184
Con Edison Transmission
Segment Reporting Information [Line Items]
Revenues			1	0
Depreciation and amortization			0	0
Operating income/(loss)	(2)	(1)	(6)	(1)
CECONY
Segment Reporting Information [Line Items]
Revenues	2,799	2,828	7,948	7,741
Depreciation and amortization	300	278	891	825
Operating income/(loss)	800	766	1,891	1,799
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	232	217	690	645
Operating income/(loss)	855	841	1,477	1,487
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	47	41	137	118
Operating income/(loss)	(12)	(28)	362	273
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	21	20	64	62
Operating income/(loss)	(43)	(47)	52	39
O&R
Segment Reporting Information [Line Items]
Depreciation and amortization	18	17	53	50
Operating income/(loss)	45	48	116	114
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	13	12	38	37
Operating income/(loss)	56	55	83	86
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	5	5	15	13
Operating income/(loss)	(11)	(7)	33	28
Operating segment
Segment Reporting Information [Line Items]
Revenues	3,211	3,417	9,072	9,368
Operating segment | Clean Energy Businesses
Segment Reporting Information [Line Items]
Revenues	177	350	460	998
Operating segment | CECONY
Segment Reporting Information [Line Items]
Revenues	2,799	2,828	7,948	7,741
Operating segment | CECONY | Electric
Segment Reporting Information [Line Items]
Revenues	2,469	2,557	6,079	6,222
Operating segment | CECONY | Gas
Segment Reporting Information [Line Items]
Revenues	268	208	1,421	1,113
Operating segment | CECONY | Steam
Segment Reporting Information [Line Items]
Revenues	62	63	448	406
Operating segment | O&R
Segment Reporting Information [Line Items]
Revenues	234	240	667	630
Operating segment | O&R | Electric
Segment Reporting Information [Line Items]
Revenues	206	213	495	497
Operating segment | O&R | Gas
Segment Reporting Information [Line Items]
Revenues	28	27	172	133
Other
Segment Reporting Information [Line Items]
Revenues	0	(1)	(4)	(1)
Depreciation and amortization	0	(1)	0	0
Operating income/(loss)	1	2	2	1
Inter-segment
Segment Reporting Information [Line Items]
Revenues	0	2	0	(7)
Inter-segment | Clean Energy Businesses
Segment Reporting Information [Line Items]
Revenues	0	(2)	0	7
Inter-segment | CECONY
Segment Reporting Information [Line Items]
Revenues	(25)	(28)	(72)	(82)
Inter-segment | CECONY | Electric
Segment Reporting Information [Line Items]
Revenues	4	5	12	13
Inter-segment | CECONY | Gas
Segment Reporting Information [Line Items]
Revenues	2	1	5	4
Inter-segment | CECONY | Steam
Segment Reporting Information [Line Items]
Revenues	$ 19	$ 22	$ 55	$ 65