Pension Benefits - Total Periodic Benefit Costs (Detail) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 74	$ 57	$ 149	$ 113
Interest cost on projected benefit obligation	144	143	287	286
Expected return on plan assets	(222)	(208)	(443)	(416)
Recognition of net actuarial loss	194	154	388	309
Recognition of prior service costs	1	1	2	2
NET PERIODIC BENEFIT COST	191	147	383	294
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	192	148	384	295
Cost capitalized	(76)	(57)	(144)	(109)
Reconciliation to rate level	(17)	30	(42)	57
Cost charged to operating expenses	99	121	198	243
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	70	53	139	106
Interest cost on projected benefit obligation	135	134	269	268
Expected return on plan assets	(210)	(198)	(420)	(395)
Recognition of net actuarial loss	183	146	367	293
Recognition of prior service costs	0	1	1	1
NET PERIODIC BENEFIT COST	178	136	356	273
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	179	137	357	274
Cost capitalized	(72)	(54)	(137)	(103)
Reconciliation to rate level	(18)	28	(42)	51
Cost charged to operating expenses	$ 89	$ 111	$ 178	$ 222