Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	$ 1,886	$ 1,905
Regulatory liabilities – current	64	128
Total Regulatory Liabilities	1,950	2,033
Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	786	755
Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	206	193
Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	164	145
Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	148	178
Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	88	60
Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	80	95
Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	55	68
New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	53	61
Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	43	55
Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	31	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	22	39
Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	12	16
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	171	173
Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	29	29
Revenue decoupling mechanism
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	29	71
Deferred derivative gains
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	6	28
CECONY
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	1,686	1,712
Regulatory liabilities – current	42	90
Total Regulatory Liabilities	1,728	1,802
CECONY | Allowance for cost of removal less salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	661	641
CECONY | Pension and other postretirement benefit deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	177	162
CECONY | Net unbilled revenue deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	164	145
CECONY | Property tax reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	148	178
CECONY | Unrecognized other postretirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	88	60
CECONY | Settlement of prudence proceeding
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	80	95
CECONY | Carrying charges on repair allowance and bonus depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	54	67
CECONY | New York State income tax rate change
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	52	60
CECONY | Variable-rate tax-exempt debt – cost rate reconciliation
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	38	48
CECONY | Base rate change deferrals
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	31	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	13	28
CECONY | Net utility plant reconciliations
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	10	15
CECONY | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities – noncurrent	143	146
CECONY | Refundable energy costs
Regulatory Liabilities [Line Items]
Regulatory liabilities – current	10	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	$ 5	$ 24