Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,378	$ 4,513
Regulatory liabilities – current	85	36
Total Regulatory Liabilities	4,463	4,549
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,153	2,207
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,089	1,090
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	251	295
Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	128	137
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	89	198
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	79	1
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	89	85
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	66	64
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	37	36
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	12	11
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	13	21
Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	16
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	14	15
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	5
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	306	302
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	58	28
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	27	8
Workers' compensation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3	3
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3,955	4,094
Regulatory liabilities – current	58	11
Total Regulatory Liabilities	4,013	4,105
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,009	2,062
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	929	932
CECONY | TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	244	286
CECONY | Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	128	137
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	89	198
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	78	0
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	46
CECONY | System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	59	57
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	35
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	23	25
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	13	21
CECONY | Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	16
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	10
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	5
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	266	261
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	33	4
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	25	7
CECONY | Workers' compensation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 3	$ 3