Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,827	$ 4,641
Regulatory liabilities—current	102	114
Total Regulatory Liabilities	4,929	4,755
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,426	2,515
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	989	928
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	471	434
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	122	127
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	199	117
Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	173	6
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	75	62
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	45	45
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	8	37
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	36
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	22	36
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	27
BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	18
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	15
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	9	7
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	203	231
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	24	53
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	44	31
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	34	30
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	4,427	4,258
Regulatory liabilities—current	63	73
Total Regulatory Liabilities	4,490	4,331
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,275	2,363
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	843	790
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	454	411
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	118	122
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	199	117
CECONY | Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	173	6
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	46	40
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	45	45
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	8	37
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	36
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	27
CECONY | System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	24
CECONY | BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	26	18
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	15
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	7
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	171	200
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	17	36
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	12	8
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	$ 34	$ 29