Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,523	$ 4,577
Regulatory liabilities – current	90	101
Total Regulatory Liabilities	4,613	4,678
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,531	2,545
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	853	846
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	178	207
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	127	127
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	112	0
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	106	183
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	97	107
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	77	92
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	58	66
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	44
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	43
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	31	36
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	25	27
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	24	30
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	20	29
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	18	21
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	12
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	176	162
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	63	41
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	18	29
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	9	31
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	4,154	4,219
Regulatory liabilities – current	54	65
Total Regulatory Liabilities	4,208	4,284
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,376	2,390
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	724	719
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	153	181
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	122	122
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	100	0
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	106	183
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	97	107
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	77	92
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	58	66
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	44
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	42
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	31	35
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	25	27
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	26
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	19
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	18	21
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	8
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	151	137
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	37	16
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	11	21
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	$ 6	$ 28