Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	$ 6,769	$ 7,024
Regulatory assets – current	109	100
Total Regulatory Assets	6,878	7,124
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,626	2,874
Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,419	2,439
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	803	823
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	341	295
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	88	48
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	70	38
Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	57	44
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	43	56
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	39	43
Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	32	50
O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	29	37
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	28	29
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	25
Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	18	28
Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	24
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	12	13
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	10	15
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	4	42
Regulatory assets – current	28	9
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	113	101
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	81	91
CECONY
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	6,248	6,473
Regulatory assets – current	100	90
Total Regulatory Assets	6,348	6,563
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,476	2,730
CECONY | Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,308	2,325
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	690	711
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	325	280
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	78	42
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	45	7
CECONY | Municipal infrastructure support costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	57	44
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	3
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	41
CECONY | Indian Point Energy Center program costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	32	50
CECONY | O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	28	29
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	25
CECONY | Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	16	26
CECONY | Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	24
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	12	13
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	4	38
Regulatory assets – current	25	4
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	103	85
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 75	$ 86