Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 1,905	$ 1,977
Regulatory liabilities—current	128	115
Total Regulatory Liabilities	2,033	2,092
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	7,024	8,096
Regulatory assets – current	100	132
Total Regulatory Assets	7,124	8,228
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	755	676
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	193	76
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	178	303
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	145	109
Prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	95	99
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	68	49
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	61	75
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	60	28
Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	55	70
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	40	128
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	39	80
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	16	32
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	44
World Trade Center settlement proceeds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	21
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	199	187
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	71	45
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	29	64
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	28	6
Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,874	3,876
Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,439	2,350
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	823	904
Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	295	253
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	56	185
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	48	50
Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	43	50
Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	42	16
Regulatory assets – current	9	19
Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	38	45
O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	37	46
Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	28	44
Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	25	26
Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	44
O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	15	21
Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	11
Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	224	175
Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	91	113
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,712	1,789
Regulatory liabilities—current	90	84
Total Regulatory Liabilities	1,802	1,873
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	6,473	7,482
Regulatory assets – current	90	121
Total Regulatory Assets	6,563	7,603
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	641	570
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	162	46
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	178	303
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	145	109
CECONY | Prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	95	99
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	67	48
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	60	72
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	60	28
CECONY | Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	60
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	40	128
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	28	80
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	31
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1	44
CECONY | World Trade Center settlement proceeds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	0	21
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	172	150
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	61	45
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	5	33
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	24	6
CECONY | Unrecognized pension and other postretirement costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,730	3,697
CECONY | Future income tax
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	2,325	2,232
CECONY | Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	711	800
CECONY | Revenue taxes
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	280	240
CECONY | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	3	110
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	42	46
CECONY | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	41	48
CECONY | Recoverable energy costs
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	38	15
Regulatory assets – current	4	18
CECONY | Pension and other postretirement benefits deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	7	16
CECONY | O&R property tax reconciliation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Surcharge for New York State assessment
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	26	40
CECONY | Preferred stock redemption
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	25	26
CECONY | Net electric deferrals
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	24	44
CECONY | O&R transition bond charges
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	0	0
CECONY | Workers’ compensation
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	13	11
CECONY | Other
Regulatory Assets [Line Items]
Regulatory assets – noncurrent	208	157
CECONY | Deferred derivative losses
Regulatory Assets [Line Items]
Regulatory assets – current	$ 86	$ 103