Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory assets	$ 4,294	$ 4,266
Regulatory liabilities – noncurrent	4,641	4,577
Regulatory liabilities—current	114	101
Total Regulatory Liabilities	4,755	4,678
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,515	2,545
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	928	846
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	434	0
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	127	127
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	117	183
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	62	207
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	45	44
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	37	66
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	107
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	29
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	12
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	43
BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	18	9
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	36
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	27
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	21
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	7	92
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3	12
Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	30
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	185	141
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	53	29
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	31	41
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	30	31
CECONY
Regulatory Liabilities [Line Items]
Regulatory assets	3,923	3,863
Regulatory liabilities – noncurrent	4,258	4,219
Regulatory liabilities—current	73	65
Total Regulatory Liabilities	4,331	4,284
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,363	2,390
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	790	719
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	411	0
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	122	122
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	117	183
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	40	181
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	45	44
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	37	66
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	107
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	19
CECONY | System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	24	11
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	42
CECONY | BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	18	9
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	35
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	27
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	21
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	7	92
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	8
CECONY | Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	26
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	156	117
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	36	21
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	8	16
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	$ 29	$ 28