Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 1,854	$ 1,905
Regulatory liabilities – current	129	128
Total Regulatory Liabilities	1,983	2,033
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	7,074	7,024
Regulatory assets – current	95	100
Total Regulatory Assets	7,169	7,124
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	772	755
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	197	193
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	162	178
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	104	145
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	91	60
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	87	95
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	62	68
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	56	61
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	50	55
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	40
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	20	39
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	16
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	175	173
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	60	29
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	41	71
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	28	28
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,911	2,874
Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,434	2,439
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	808	823
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	307	295
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	68	48
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	53	56
Municipal infrastructure support cost
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	49	44
Indian Point Energy Center
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	48	50
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	48	38
Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	45	28
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	42	43
O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	35	37
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	29	42
Regulatory assets – current	4	9
Brooklyn Queens demand management program
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	28	29
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	25	25
Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	20	24
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	14	13
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	15
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	97	101
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	91	91
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,654	1,712
Regulatory liabilities – current	96	90
Total Regulatory Liabilities	1,750	1,802
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	6,520	6,473
Regulatory assets – current	85	90
Total Regulatory Assets	6,605	6,563
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	649	641
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	167	162
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	162	178
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	104	145
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	91	60
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	87	95
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	61	67
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	55	60
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	48
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	40
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	28
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	13	15
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	148	146
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	36	5
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	38	61
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	22	24
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,748	2,730
CECONY | Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,321	2,325
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	697	711
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	291	280
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	62	42
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3	3
CECONY | Municipal infrastructure support cost
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	49	44
CECONY | Indian Point Energy Center
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	48	50
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	19	7
CECONY | Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	42	26
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	40	41
CECONY | O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	26	38
Regulatory assets – current	0	4
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	25	25
CECONY | Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	20	24
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	14	13
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	87	85
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 85	$ 86