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Income Tax - Additional Information (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in net deferred tax liabilities resulting from TCJA |  | $ 13,000,000 | $ 5,312,000,000
Change in net income resulting from TCJA |  |  | 259,000,000
Charitable contribution carryforwards | $ 28,000,000 |  |
Deferred tax asset, valuation allowance | 40,000,000 | 33,000,000 |
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years | 2,000,000 | 3,000,000 | 6,000,000
Effective income tax rate reconciliation, uncertainty of taxes | 10,000,000 |  |
Penalties for uncertain tax positions | 0 | 0 |
Amount of interest and penalties in their consolidated balance sheets | 0 | 0 |
Unrecognized tax benefits that would have an impact on effective tax rate | 13,000,000 |  |
Unrecognized tax benefits that would have an impact on effective tax rate, net of tax | 12,000,000 |  |
General Business Tax Credit |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Tax credit carryovers | 896,000,000 |  |
Operating loss carryforwards, valuation allowance | 0 |  |
Tax Year 2015 |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Charitable contribution carryforwards | 5,000,000 |  |
Tax Year 2016 |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Charitable contribution carryforwards | 7,000,000 |  |
Tax Year 2017 |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Charitable contribution carryforwards | 5,000,000 |  |
Tax Year 2018 |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Charitable contribution carryforwards | 5,000,000 |  |
Tax Year 2019 |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Charitable contribution carryforwards | 6,000,000 |  |
Federal |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Additional depreciation deducted |  |  | 477,000,000
Operating loss carryforwards | 36,000,000 |  | 563,000,000
Operating loss carryover subject to expiration |  | 13,000,000 |
Operating loss carryover not subject to expiration | 23,000,000 |  |
State | New York State |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards |  | 272,000,000 |
Operating loss carryforwards, valuation allowance | 22,000,000 |  |
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years | 4,000,000 |  |
State | New York City |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards, valuation allowance | 18,000,000 |  |
State | Carry Back to 2015 and 2016 | New York State |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards | 100,000,000 |  |
Income tax recovery resulting from operating loss carry back | 9,000,000 |  |
State | Carried Forward to Future Years | New York State |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards | 172,000,000 |  |
State | Tax Year 2019 | New York State |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards | 453,000,000 |  |
Parent Company |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Change in net income resulting from TCJA |  | 42,000,000 | (21,000,000)
Clean Energy Businesses |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Change in net income resulting from TCJA |  |  | 269,000,000
Con Edison Transmission |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Change in net income resulting from TCJA |  |  | 11,000,000
Future Income Tax |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Increase in regulatory liability resulting from TCJA |  | 54,000,000 | 3,713,000,000
Accelerated Tax Depreciation Benefits |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Increase in regulatory liability resulting from TCJA |  |  | 2,684,000,000
Future Income Tax |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in regulatory asset resulting from TCJA |  |  | 1,250,000,000
Revenue Taxes |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in regulatory asset resulting from TCJA |  |  | 90,000,000
CECONY |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in net deferred tax liabilities resulting from TCJA |  | 50,000,000 | 4,781,000,000
Deferred tax asset, valuation allowance | 0 | 0 |
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years | 2,000,000 | 3,000,000 | 0
Effective income tax rate reconciliation, uncertainty of taxes | 1,000,000 |  |
Unrecognized tax benefits that would have an impact on effective tax rate | 2,000,000 |  |
CECONY | New York State |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years | $ 2,000,000 |  |
CECONY | Federal |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Operating loss carryforwards |  |  | 153,000,000
CECONY | Future Income Tax |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Increase in regulatory liability resulting from TCJA |  | 49,000,000 | 3,513,000,000
CECONY | Accelerated Tax Depreciation Benefits |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Increase in regulatory liability resulting from TCJA |  |  | 2,542,000,000
CECONY | Future Income Tax |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in regulatory asset resulting from TCJA |  |  | 1,182,000,000
CECONY | Revenue Taxes |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Decrease in regulatory asset resulting from TCJA |  | $ 1,000,000 | $ 86,000,000

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