Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 3,950	$ 4,266
Regulatory assets – current	25	67
Total Regulatory Assets	3,975	4,333
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,001	2,526
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	754	793
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	287	260
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	189	50
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	85	51
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	80	38
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	73	79
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	73	56
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	62	60
Regulatory assets – current	6	27
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	37
Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	18
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	30	37
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	23	24
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	21	44
Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	13
Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	18	19
Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	29
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	6	10
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3	9
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	138	113
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	19	40
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3,576	3,863
Regulatory assets – current	19	62
Total Regulatory Assets	3,595	3,925
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	1,881	2,376
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	653	677
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	274	248
CECONY | MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	189	50
CECONY | Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	68	25
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	56	58
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	73	56
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	57	52
Regulatory assets – current	5	25
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	35
CECONY | Meadowlands heater odorization project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	36	18
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	30	37
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	23	24
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	37
CECONY | Gate station upgrade project
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	13
CECONY | Recoverable REV demonstration project costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	17
CECONY | Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	29
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	6	10
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	128	101
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 14	$ 37