Financial Information by Business Segment - Financial Data for Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 2,788	$ 2,911	$ 6,404	$ 6,700
Depreciation and amortization	276	265	555	526
Operating income	472	455	1,198	1,140
CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,283	2,436	5,292	5,641
Depreciation and amortization	254	247	511	486
Operating income	460	386	1,143	1,030
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	201	195	403	383
Operating income	422	347	700	605
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	35	33	70	64
Operating income	54	54	294	287
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	18	19	38	39
Operating income	(16)	(15)	149	138
O&R
Segment Reporting Information [Line Items]
Depreciation and amortization	17	15	34	29
Operating income	(2)	20	43	59
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	13	11	25	21
Operating income	16	25	34	37
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	9	8
Operating income	(18)	(5)	9	22
Competitive energy businesses
Segment Reporting Information [Line Items]
Depreciation and amortization	6	4	11	11
Operating income	13	48	10	50
Other
Segment Reporting Information [Line Items]
Depreciation and amortization	(1)	(1)	(1)
Operating income	1	1	2	1
Operating revenues
Segment Reporting Information [Line Items]
Operating revenues	2,788	2,911	6,404	6,700
Operating revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,283	2,436	5,292	5,641
Operating revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	1,879	1,978	3,858	4,053
Operating revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	308	360	963	1,149
Operating revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	96	98	471	439
Operating revenues | O&R
Segment Reporting Information [Line Items]
Operating revenues	178	192	411	448
Operating revenues | O&R | Electric
Segment Reporting Information [Line Items]
Operating revenues	162	157	318	320
Operating revenues | O&R | Gas
Segment Reporting Information [Line Items]
Operating revenues	16	35	93	128
Operating revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	328	284	702	612
Operating revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	(1)	(1)	(1)	(1)
Inter-segment revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	(27)	(27)	(55)	(52)
Inter-segment revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	5	4	9	8
Inter-segment revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	1	2	3	3
Inter-segment revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	21	21	43	41
Inter-segment revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	(1)	(1)	(4)	1
Inter-segment revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	$ 1	$ 1	$ 4	$ (1)