Regulatory Matters - Regulatory Assets and Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Regulatory assets
Regulatory assets – noncurrent	$ 7,680	$ 8,096
Regulatory assets – current	84	132
Total Regulatory Assets	7,764	8,228
Regulatory liabilities
Regulatory liabilities – noncurrent	1,932	1,977
Regulatory liabilities – current	122	115
Total Regulatory Liabilities	2,054	2,092
Allowance for cost of removal less salvage
Regulatory liabilities
Regulatory liabilities – noncurrent	708	676
Property tax reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	230	303
Pension and other postretirement benefit deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	125	76
Net unbilled revenue deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	117	109
Prudence proceeding
Regulatory liabilities
Regulatory liabilities – noncurrent		99
Unrecognized other postretirement costs
Regulatory liabilities
Regulatory liabilities – noncurrent	93	28
Base rate change deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	77	128
New York State income tax rate change
Regulatory liabilities
Regulatory liabilities – noncurrent	69	75
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	64	70
Carrying charges on repair allowance and bonus depreciation
Regulatory liabilities
Regulatory liabilities – noncurrent	51	49
Earnings sharing - electric, gas and steam
Regulatory liabilities
Regulatory liabilities – noncurrent	34	80
Net utility plant reconciliations
Regulatory liabilities
Regulatory liabilities – noncurrent	28	32
Property tax refunds
Regulatory liabilities
Regulatory liabilities – noncurrent	22	44
World Trade Center settlement proceeds
Regulatory liabilities
Regulatory liabilities – noncurrent	10	21
Other
Regulatory liabilities
Regulatory liabilities – noncurrent	207	187
Revenue decoupling mechanism
Regulatory liabilities
Regulatory liabilities – current	79	45
Refundable energy costs
Regulatory liabilities
Regulatory liabilities – current	30	64
Deferred derivative gains
Regulatory liabilities
Regulatory liabilities – current	13	6
Unrecognized pension and other postretirement costs
Regulatory assets
Regulatory assets – noncurrent	3,516	3,876
Future income tax
Regulatory assets
Regulatory assets – noncurrent	2,379	2,350
Revenue taxes
Regulatory assets
Regulatory assets – noncurrent	295	253
Deferred storm costs
Regulatory assets
Regulatory assets – noncurrent	122	185
Unamortized loss on reacquired debt
Regulatory assets
Regulatory assets – noncurrent	47	50
O&R property tax reconciliation
Regulatory assets
Regulatory assets – noncurrent	42	46
Deferred derivative losses
Regulatory assets
Regulatory assets – noncurrent	38	50
Pension and other postretirement benefits deferrals
Regulatory assets
Regulatory assets – noncurrent	35	45
Net electric deferrals
Regulatory assets
Regulatory assets – noncurrent	34	44
Surcharge for New York State assessment
Regulatory assets
Regulatory assets – noncurrent	32	44
Preferred stock redemption
Regulatory assets
Regulatory assets – noncurrent	26	26
O&R transition bond charges
Regulatory assets
Regulatory assets – noncurrent	18	21
Recoverable energy costs
Regulatory assets
Regulatory assets – noncurrent	0	16
Regulatory assets – current	9	19
Other
Regulatory assets
Regulatory assets – noncurrent	243	175
Deferred derivative losses
Regulatory assets
Regulatory assets – current	75	113
CECONY
Regulatory assets
Regulatory assets – noncurrent	7,109	7,482
Regulatory assets – current	77	121
Total Regulatory Assets	7,186	7,603
Regulatory liabilities
Regulatory liabilities – noncurrent	1,743	1,789
Regulatory liabilities – current	98	84
Total Regulatory Liabilities	1,841	1,873
CECONY | Allowance for cost of removal less salvage
Regulatory liabilities
Regulatory liabilities – noncurrent	599	570
CECONY | Property tax reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	230	303
CECONY | Pension and other postretirement benefit deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	96	46
CECONY | Net unbilled revenue deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	117	109
CECONY | Prudence proceeding
Regulatory liabilities
Regulatory liabilities – noncurrent	97	99
CECONY | Unrecognized other postretirement costs
Regulatory liabilities
Regulatory liabilities – noncurrent	93	28
CECONY | Base rate change deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	77	128
CECONY | New York State income tax rate change
Regulatory liabilities
Regulatory liabilities – noncurrent	66	72
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	56	60
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory liabilities
Regulatory liabilities – noncurrent	50	48
CECONY | Earnings sharing - electric, gas and steam
Regulatory liabilities
Regulatory liabilities – noncurrent	30	80
CECONY | Net utility plant reconciliations
Regulatory liabilities
Regulatory liabilities – noncurrent	28	31
CECONY | Property tax refunds
Regulatory liabilities
Regulatory liabilities – noncurrent	22	44
CECONY | World Trade Center settlement proceeds
Regulatory liabilities
Regulatory liabilities – noncurrent	10	21
CECONY | Other
Regulatory liabilities
Regulatory liabilities – noncurrent	172	150
CECONY | Revenue decoupling mechanism
Regulatory liabilities
Regulatory liabilities – current	78	45
CECONY | Refundable energy costs
Regulatory liabilities
Regulatory liabilities – current	9	33
CECONY | Deferred derivative gains
Regulatory liabilities
Regulatory liabilities – current	11	6
CECONY | Unrecognized pension and other postretirement costs
Regulatory assets
Regulatory assets – noncurrent	3,361	3,697
CECONY | Future income tax
Regulatory assets
Regulatory assets – noncurrent	2,262	2,232
CECONY | Revenue taxes
Regulatory assets
Regulatory assets – noncurrent	281	240
CECONY | Deferred storm costs
Regulatory assets
Regulatory assets – noncurrent	57	110
CECONY | Unamortized loss on reacquired debt
Regulatory assets
Regulatory assets – noncurrent	44	48
CECONY | O&R property tax reconciliation
Regulatory assets
Regulatory assets – noncurrent	0	0
CECONY | Deferred derivative losses
Regulatory assets
Regulatory assets – noncurrent	35	46
CECONY | Pension and other postretirement benefits deferrals
Regulatory assets
Regulatory assets – noncurrent	6	16
CECONY | Net electric deferrals
Regulatory assets
Regulatory assets – noncurrent	34	44
CECONY | Surcharge for New York State assessment
Regulatory assets
Regulatory assets – noncurrent	29	40
CECONY | Preferred stock redemption
Regulatory assets
Regulatory assets – noncurrent	26	26
CECONY | O&R transition bond charges
Regulatory assets
Regulatory assets – noncurrent	0	0
CECONY | Recoverable energy costs
Regulatory assets
Regulatory assets – noncurrent	0	15
Regulatory assets – current	7	18
CECONY | Other
Regulatory assets
Regulatory assets – noncurrent	226	157
CECONY | Deferred derivative losses
Regulatory assets
Regulatory assets – current	70	103
Superfund Sites
Regulatory assets
Total Regulatory Assets	837	904
Superfund Sites | Environmental remediation costs
Regulatory assets
Regulatory assets – noncurrent	837	904
Superfund Sites | CECONY
Regulatory assets
Total Regulatory Assets	732	800
Superfund Sites | CECONY | Environmental remediation costs
Regulatory assets
Regulatory assets – noncurrent	732	800
Workers’ compensation
Regulatory assets
Total Regulatory Assets	16	11
Workers’ compensation | Workers’ compensation
Regulatory assets
Regulatory assets – noncurrent	16	11
Workers’ compensation | CECONY
Regulatory assets
Total Regulatory Assets	16	11
Workers’ compensation | CECONY | Workers’ compensation
Regulatory assets
Regulatory assets – noncurrent	$ 16	$ 11