Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 4,266	$ 7,024
Regulatory assets – current	67	100
Total Regulatory Assets	4,333	7,124
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,526	2,874
Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	2,439
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	793	823
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	260	295
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	79	38
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	60	42
Regulatory assets – current	27	9
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	56	44
Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	51	37
MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	50	0
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	44	48
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	38	56
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	29
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	43
Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	29	50
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	25
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	10	13
Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	9	24
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	9	15
Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2	28
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	152	101
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	40	91
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3,863	6,473
Regulatory assets – current	62	90
Total Regulatory Assets	3,925	6,563
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,376	2,730
CECONY | Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	2,325
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	677	711
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	248	280
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	58	7
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	52	38
Regulatory assets – current	25	4
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	56	44
CECONY | Property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	25	0
CECONY | MTA power reliability deferral
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	50	0
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	42
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	3
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	29
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	41
CECONY | Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	29	50
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	25
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	10	13
CECONY | Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	9	24
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	2	26
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	138	85
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 37	$ 86