Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,379	$ 4,513
Regulatory liabilities – current	490	36
Total Regulatory Liabilities	4,869	4,549
Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3,941	4,094
Regulatory liabilities – current	428	11
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,040	2,207
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,114	1,090
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	184	198
TCJA net benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	167	295
Net proceeds from sale of property
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	111	137
Deferred derivative gains - long term
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	110	5
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	98	85
System benefit charge carrying charge
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	71	64
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	1
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	36
BQDM and REV Demo reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	26	27
Sales and use tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	18	16
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	13	15
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	12	11
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	11	21
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	5
Workers' compensation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	5	3
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	341	297
Deferred derivative gains - short term
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	451	8
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	31	28
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	8	0
CECONY | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	3,941	4,094
Regulatory liabilities – current	428	11
Total Regulatory Liabilities	4,369	4,105
CECONY | Future income tax | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,896	2,062
CECONY | Allowance for cost of removal less salvage | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	950	932
CECONY | Net unbilled revenue deferrals | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	184	198
CECONY | TCJA net benefits | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	164	286
CECONY | Net proceeds from sale of property | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	111	137
CECONY | Deferred derivative gains - long term | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	101	4
CECONY | Pension and other postretirement benefit deferrals | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	53	46
CECONY | System benefit charge carrying charge | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	63	57
CECONY | Energy efficiency portfolio standard unencumbered funds | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	19	0
CECONY | Property tax refunds | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	35
CECONY | BQDM and REV Demo reconciliations | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	22	25
CECONY | Sales and use tax refunds | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	17	16
CECONY | Earnings sharing - electric, gas and steam | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	10
CECONY | Unrecognized other postretirement costs | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	0
CECONY | Settlement of gas proceedings | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	11	21
CECONY | Settlement of prudence proceeding | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	6	5
CECONY | Workers' compensation | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	5	3
CECONY | Other | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	294	257
CECONY | Deferred derivative gains - short term | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	423	7
CECONY | Refundable energy costs | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	5	4
CECONY | Revenue decoupling mechanism | Subsidiaries
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	$ 0	$ 0