Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 4,577	$ 1,905
Regulatory liabilities—current	101	128
Total Regulatory Liabilities	4,678	2,033
Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,545	0
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	846	755
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	207	193
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	183	145
Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	127	0
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	107	178
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	92	60
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	66	95
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	1
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	43	68
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	61
Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	30	55
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	29	39
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	40
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	12	16
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	162	172
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	41	29
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	31	28
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	29	71
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	4,219	1,712
Regulatory liabilities—current	65	90
Total Regulatory Liabilities	4,284	1,802
CECONY | Future income tax
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	2,390	0
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	719	641
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	181	162
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	183	145
CECONY | Energy efficiency portfolio standard unencumbered funds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	122	0
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	107	178
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	92	60
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	66	95
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	44	1
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	42	67
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	35	60
CECONY | Variable-rate tax-exempt debt - cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	26	48
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	19	28
CECONY | Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	21	40
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	8	15
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	137	145
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	16	5
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	28	24
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities—current	$ 21	$ 61