Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 4,284	$ 4,266
Regulatory assets – current	123	67
Total Regulatory Assets	4,407	4,333
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,332	2,526
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	783	793
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	271	260
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	122	50
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	118	60
Regulatory assets – current	35	27
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	95	44
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	77	79
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	64	51
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	59	56
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	37
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	60	38
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	32	37
Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	30	18
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	24
Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	29
Recoverable REV demonstration project expenses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	19
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	13
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	10	10
Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	9	9
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	7	9
Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	2
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	102	102
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	88	40
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3,871	3,863
Regulatory assets – current	115	62
Total Regulatory Assets	3,986	3,925
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,196	2,376
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	668	677
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	259	248
CECONY | MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	122	50
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	103	52
Regulatory assets – current	34	25
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	86	37
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	57	58
CECONY | Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	41	25
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	59	56
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	34	35
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	32	37
CECONY | Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	30	18
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	24
CECONY | Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	29
CECONY | Recoverable REV demonstration project expenses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	17	17
CECONY | Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	13
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	10	10
CECONY | Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	9	9
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	2
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	90	90
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 81	$ 37