Regulatory Matters - Regulatory Assets and Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Regulatory assets
Regulatory assets – noncurrent	$ 8,646	$ 9,156
Regulatory assets – current	75	148
Total Regulatory Assets	8,721	9,304
Regulatory liabilities
Regulatory liabilities – noncurrent	1,947	1,993
Regulatory liabilities – current	142	187
Total Regulatory Liabilities	2,089	2,180
Unrecognized pension and other postretirement costs
Regulatory assets
Regulatory assets – noncurrent	4,400	4,846
Future income tax
Regulatory assets
Regulatory assets – noncurrent	2,326	2,273
Deferred storm costs
Regulatory assets
Regulatory assets – noncurrent	254	319
Revenue taxes
Regulatory assets
Regulatory assets – noncurrent	227	219
Pension and other postretirement benefits deferrals
Regulatory assets
Regulatory assets – noncurrent	54	66
Net electric deferrals
Regulatory assets
Regulatory assets – noncurrent	54	63
Unamortized loss on reacquired debt
Regulatory assets
Regulatory assets – noncurrent	54	57
Deferred derivative losses
Regulatory assets
Regulatory assets – noncurrent	46	25
Surcharge for New York State assessment
Regulatory assets
Regulatory assets – noncurrent	40	99
O&R property tax reconciliation
Regulatory assets
Regulatory assets – noncurrent	40	36
Preferred stock redemption
Regulatory assets
Regulatory assets – noncurrent	27	27
O&R transition bond charges
Regulatory assets
Regulatory assets – noncurrent	24	27
Recoverable energy costs
Regulatory assets
Regulatory assets – noncurrent	0	19
Regulatory assets – current	2	41
Other
Regulatory assets
Regulatory assets – noncurrent	193	147
Deferred derivative losses
Regulatory assets
Regulatory assets – current	65	97
Future income tax
Regulatory assets
Regulatory assets – current	8	10
Allowance for cost of removal less salvage
Regulatory liabilities
Regulatory liabilities – noncurrent	620	598
Property tax reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	300	295
Base rate change deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	146	155
Net unbilled revenue deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	116	138
Prudence proceeding
Regulatory liabilities
Regulatory liabilities – noncurrent	103	105
Pension and other postretirement benefit deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	83	46
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	80	78
Property tax refunds
Regulatory liabilities
Regulatory liabilities – noncurrent	65	87
New York State income tax rate change
Regulatory liabilities
Regulatory liabilities – noncurrent	64	62
Carrying charges on repair allowance and bonus depreciation
Regulatory liabilities
Regulatory liabilities – noncurrent	52	58
World Trade Center settlement proceeds
Regulatory liabilities
Regulatory liabilities – noncurrent	31	41
Net utility plant reconciliations
Regulatory liabilities
Regulatory liabilities – noncurrent	22	21
Earnings sharing – electric
Regulatory liabilities
Regulatory liabilities – noncurrent	21	19
Unrecognized other postretirement costs
Regulatory liabilities
Regulatory liabilities – noncurrent	17	0
Other
Regulatory liabilities
Regulatory liabilities – noncurrent	227	290
Refundable energy costs
Regulatory liabilities
Regulatory liabilities – current	72	128
Revenue decoupling mechanism
Regulatory liabilities
Regulatory liabilities – current	42	30
Future income tax
Regulatory liabilities
Regulatory liabilities – current	22	24
Deferred derivative gains
Regulatory liabilities
Regulatory liabilities – current	6	5
CECONY
Regulatory assets
Regulatory assets – noncurrent	8,011	8,481
Regulatory assets – current	60	132
Total Regulatory Assets	8,071	8,613
Regulatory liabilities
Regulatory liabilities – noncurrent	1,772	1,837
Regulatory liabilities – current	107	142
Total Regulatory Liabilities	1,879	1,979
CECONY | Unrecognized pension and other postretirement costs
Regulatory assets
Regulatory assets – noncurrent	4,191	4,609
CECONY | Future income tax
Regulatory assets
Regulatory assets – noncurrent	2,216	2,166
CECONY | Deferred storm costs
Regulatory assets
Regulatory assets – noncurrent	167	224
CECONY | Revenue taxes
Regulatory assets
Regulatory assets – noncurrent	215	208
CECONY | Pension and other postretirement benefits deferrals
Regulatory assets
Regulatory assets – noncurrent	27	42
CECONY | Net electric deferrals
Regulatory assets
Regulatory assets – noncurrent	53	63
CECONY | Unamortized loss on reacquired debt
Regulatory assets
Regulatory assets – noncurrent	51	55
CECONY | Deferred derivative losses
Regulatory assets
Regulatory assets – noncurrent	41	23
CECONY | Surcharge for New York State assessment
Regulatory assets
Regulatory assets – noncurrent	38	92
CECONY | O&R property tax reconciliation
Regulatory assets
Regulatory assets – noncurrent	0	0
CECONY | Preferred stock redemption
Regulatory assets
Regulatory assets – noncurrent	27	27
CECONY | O&R transition bond charges
Regulatory assets
Regulatory assets – noncurrent	0	0
CECONY | Recoverable energy costs
Regulatory assets
Regulatory assets – noncurrent	0	17
Regulatory assets – current	0	40
CECONY | Other
Regulatory assets
Regulatory assets – noncurrent	179	127
CECONY | Deferred derivative losses
Regulatory assets
Regulatory assets – current	60	92
CECONY | Future income tax
Regulatory assets
Regulatory assets – current	0	0
CECONY | Allowance for cost of removal less salvage
Regulatory liabilities
Regulatory liabilities – noncurrent	518	499
CECONY | Property tax reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	300	295
CECONY | Base rate change deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	146	155
CECONY | Net unbilled revenue deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	116	138
CECONY | Prudence proceeding
Regulatory liabilities
Regulatory liabilities – noncurrent	103	105
CECONY | Pension and other postretirement benefit deferrals
Regulatory liabilities
Regulatory liabilities – noncurrent	59	37
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory liabilities
Regulatory liabilities – noncurrent	69	78
CECONY | Property tax refunds
Regulatory liabilities
Regulatory liabilities – noncurrent	65	87
CECONY | New York State income tax rate change
Regulatory liabilities
Regulatory liabilities – noncurrent	61	59
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory liabilities
Regulatory liabilities – noncurrent	50	57
CECONY | World Trade Center settlement proceeds
Regulatory liabilities
Regulatory liabilities – noncurrent	31	41
CECONY | Net utility plant reconciliations
Regulatory liabilities
Regulatory liabilities – noncurrent	23	20
CECONY | Earnings sharing – electric
Regulatory liabilities
Regulatory liabilities – noncurrent	21	18
CECONY | Unrecognized other postretirement costs
Regulatory liabilities
Regulatory liabilities – noncurrent	17	0
CECONY | Other
Regulatory liabilities
Regulatory liabilities – noncurrent	193	248
CECONY | Refundable energy costs
Regulatory liabilities
Regulatory liabilities – current	39	84
CECONY | Revenue decoupling mechanism
Regulatory liabilities
Regulatory liabilities – current	41	30
CECONY | Future income tax
Regulatory liabilities
Regulatory liabilities – current	21	24
CECONY | Deferred derivative gains
Regulatory liabilities
Regulatory liabilities – current	6	4
Superfund Sites
Regulatory assets
Total Regulatory Assets	897	925
Superfund Sites | Environmental remediation costs
Regulatory assets
Regulatory assets – noncurrent	897	925
Superfund Sites | CECONY
Regulatory assets
Total Regulatory Assets	796	820
Superfund Sites | CECONY | Environmental remediation costs
Regulatory assets
Regulatory assets – noncurrent	796	820
Workers’ compensation
Regulatory assets
Total Regulatory Assets	10	8
Workers’ compensation | Workers’ compensation
Regulatory assets
Regulatory assets – noncurrent	10	8
Workers’ compensation | CECONY
Regulatory assets
Total Regulatory Assets	10	8
Workers’ compensation | CECONY | Workers’ compensation
Regulatory assets
Regulatory assets – noncurrent	$ 10	$ 8