Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 4,655	$ 4,859
Regulatory assets – current	166	128
Total Regulatory Assets	4,821	4,987
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	1,901	2,541
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	723	732
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	345	321
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	238	219
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	274	71
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	200	248
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	156	83
System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	95	131
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	67	75
COVID-19 pandemic deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	102	0
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	158	77
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	39
Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	33	35
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	26	19
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	22	28
Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	21
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	22
Non-wire alternative projects
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	14
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	3
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	219	180
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	116	128
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	50	0
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	4,278	4,487
Regulatory assets – current	144	113
Total Regulatory Assets	4,422	4,600
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	1,785	2,403
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	645	647
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	331	308
CECONY | Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	235	210
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	237	47
CECONY | MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	200	248
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	145	76
CECONY | System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	94	130
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	67	75
CECONY | COVID-19 pandemic deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	101	0
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	60	0
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	39
CECONY | Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	33	35
CECONY | Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	26	19
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	26
CECONY | Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	22	19
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	22
CECONY | Non-wire alternative projects
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	14
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	3
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	204	166
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	104	113
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	$ 40	$ 0