Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 5,889	$ 6,195
Regulatory assets – current	184	266
Total Regulatory Assets	6,073	6,461
Regulatory assets not earning return	4,224	4,766
Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5,472	5,745
Regulatory assets – current	167	244
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,750	3,241
Regulatory assets not earning return	2,750	3,241
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	852	865
Regulatory assets not earning return	839	855
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	395	315
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	373	356
Regulatory assets not earning return	353	336
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	246	241
COVID-19 pandemic deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	239	115
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	225	195
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	164	188
System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	88	124
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	75	120
Regulatory assets not earning return	75	120
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	52	62
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	36
Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	31	32
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	21
Non-wire alternative projects
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	18
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	18	21
Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	18	20
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	25
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	272	200
Regulatory assets not earning return	46	24
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	161	190
Regulatory assets not earning return	161	190
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	23	76
CECONY | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5,472	5,745
Regulatory assets – current	167	244
Total Regulatory Assets	5,639	5,989
Regulatory assets not earning return	3,983	4,481
CECONY | Unrecognized pension and other postretirement costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,607	3,065
Regulatory assets not earning return	2,607	3,065
CECONY | Environmental remediation costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	783	791
Regulatory assets not earning return	770	781
CECONY | Pension and other postretirement benefits deferrals | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	344	272
CECONY | Revenue taxes | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	357	342
Regulatory assets not earning return	339	323
CECONY | Property tax reconciliation | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	246	239
CECONY | COVID-19 pandemic deferrals | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	234	113
CECONY | Deferred storm costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	112	83
CECONY | MTA power reliability deferral | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	164	188
CECONY | System peak reduction and energy efficiency programs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	88	124
CECONY | Deferred derivative losses | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	69	111
Regulatory assets not earning return	69	111
CECONY | Municipal infrastructure support costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	52	62
CECONY | Brooklyn Queens demand management program | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	36
CECONY | Meadowlands heater odorization project | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	31	32
CECONY | Preferred stock redemption | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	21
CECONY | Non-wire alternative projects | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	18
CECONY | Unamortized loss on reacquired debt | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	19
CECONY | Recoverable REV demonstration project costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	18
CECONY | Gate station upgrade project | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	25
CECONY | Other | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	262	186
Regulatory assets not earning return	46	24
CECONY | Deferred derivative losses | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – current	152	177
Regulatory assets not earning return	152	177
CECONY | Recoverable energy costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – current	$ 15	$ 67