Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 5,903	$ 6,195
Regulatory assets – current	205	266
Total Regulatory Assets	6,108	6,461
Regulatory assets not earning return	4,081	4,766
Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5,473	5,745
Regulatory assets – current	187	244
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,527	3,241
Regulatory assets not earning return	2,527	3,241
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	846	865
Regulatory assets not earning return	832	855
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	438	315
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	385	356
Regulatory assets not earning return	364	336
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	245	241
COVID-19 pandemic deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	274	115
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	277	195
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	152	188
System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	145	124
Deferred derivative losses - long term
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	136	120
Regulatory assets not earning return	136	120
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	49	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	30	32
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	20	21
Non-wire alternative projects
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	23	18
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	17	21
Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	20
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	25
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	274	200
Regulatory assets not earning return	56	24
Deferred derivative losses - short term
Regulatory Assets [Line Items]
Regulatory assets – current	166	190
Regulatory assets not earning return	166	190
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	39	76
CECONY | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5,473	5,745
Regulatory assets – current	187	244
Total Regulatory Assets	5,660	5,989
Regulatory assets not earning return	3,843	4,481
CECONY | Unrecognized pension and other postretirement costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,394	3,065
Regulatory assets not earning return	2,394	3,065
CECONY | Environmental remediation costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	780	791
Regulatory assets not earning return	765	781
CECONY | Pension and other postretirement benefits deferrals | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	382	272
CECONY | Revenue taxes | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	369	342
Regulatory assets not earning return	349	323
CECONY | Property tax reconciliation | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	245	239
CECONY | COVID-19 pandemic deferrals | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	269	113
CECONY | Deferred storm costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	155	83
CECONY | MTA power reliability deferral | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	152	188
CECONY | System peak reduction and energy efficiency programs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	145	124
CECONY | Deferred derivative losses - long term | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	124	111
Regulatory assets not earning return	124	111
CECONY | Municipal infrastructure support costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	49	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	30	32
CECONY | Preferred stock redemption | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	20	21
CECONY | Non-wire alternative projects | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	23	18
CECONY | Unamortized loss on reacquired debt | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	19
CECONY | Recoverable REV demonstration project costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	14	18
CECONY | Gate station upgrade project | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	25
CECONY | Other | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	257	186
Regulatory assets not earning return	56	24
CECONY | Deferred derivative losses - short term | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – current	155	177
Regulatory assets not earning return	155	177
CECONY | Recoverable energy costs | Subsidiaries
Regulatory Assets [Line Items]
Regulatory assets – current	$ 32	$ 67