Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 4,159	$ 4,294
Regulatory assets – current	83	76
Total Regulatory Assets	4,242	4,370
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	1,919	2,238
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	774	810
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	315	291
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	245	229
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	160	101
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	99	17
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	80	67
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	77	73
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	69	76
System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	60	72
Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	36
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	39
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	30	36
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	22	23
Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	20
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	17
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5	5
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	2
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	194	142
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	68	36
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	15	40
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3,831	3,923
Regulatory assets – current	69	64
Total Regulatory Assets	3,900	3,987
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	1,816	2,111
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	685	716
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	302	278
CECONY | MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	245	229
CECONY | Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	150	86
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	90	11
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	80	67
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	55	56
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | System peak reduction and energy efficiency programs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	59	70
CECONY | Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	36
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	39
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	28	34
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	22	23
CECONY | Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	18	18
CECONY | Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	17
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	5	5
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	187	127
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	57	29
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – current	$ 12	$ 35