Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 1,873	$ 1,905
Regulatory liabilities – current	58	128
Total Regulatory Liabilities	1,931	2,033
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	798	755
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	202	193
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	166	145
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	140	178
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	84	60
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	73	95
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	49	68
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	61
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	36	55
Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	28	1
Settlement of gas proceedings
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	27	27
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	26	40
Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	24	39
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	11	16
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	161	172
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	29	29
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	27	71
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	2	28
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,673	1,712
Regulatory liabilities – current	38	90
Total Regulatory Liabilities	1,711	1,802
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	671	641
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	174	162
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	166	145
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	140	178
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	84	60
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	73	95
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	67
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	48	60
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	32	48
CECONY | Property tax refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	28	1
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	26	40
CECONY | Earnings sharing - electric, gas and steam
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	15	28
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	8	15
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	133	145
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	9	5
CECONY | Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	27	61
CECONY | Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	$ 2	$ 24