Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,569	$ 4,827
Regulatory liabilities – current	90	102
Total Regulatory Liabilities	4,659	4,929
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,270	2,426
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,038	989
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	337	471
Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	152	173
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	148	199
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	65	122
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	79	75
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	60	48
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	45
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	33	9
BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	26	27
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	22	10
Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	8
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	16	22
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	8
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	265	195
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	33	44
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	57	34
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	0	24
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	4,134	4,427
Regulatory liabilities – current	62	63
Total Regulatory Liabilities	4,196	4,490
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,123	2,275
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	885	843
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	327	454
CECONY | Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	152	173
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	148	199
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	62	118
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	43	46
CECONY | System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	54	44
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	34	45
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	0
CECONY | BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	24	26
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	22	10
CECONY | Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	8
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	15
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	8
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	227	163
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	8	12
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	54	34
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	$ 0	$ 17