Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,513	$ 4,827
Regulatory liabilities—current	36	102
Total Regulatory Liabilities	4,549	4,929
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,207	2,426
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,090	989
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	295	471
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	198	199
Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	137	173
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	85	75
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	64	48
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	45
BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	10
Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	16	8
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	22
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	11	9
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	5	8
Workers’ compensation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3	0
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	122
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	302	195
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	28	44
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	8	34
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	0	24
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	4,094	4,427
Regulatory liabilities—current	11	63
Total Regulatory Liabilities	4,105	4,490
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,062	2,275
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	932	843
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	286	454
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	198	199
CECONY | Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	137	173
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	46	46
CECONY | System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	57	44
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	45
CECONY | BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	25	26
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	10
CECONY | Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	16	8
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	15
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	0
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	5	8
CECONY | Workers’ compensation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3	0
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	118
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	261	163
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	4	12
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	7	34
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	$ 0	$ 17