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Income Tax - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Operating Loss Carryforwards [Line Items] |  |  |  |
Operating loss carryforwards | $ 21.0 |  |  |
Unrecognized Tax Benefits | 14.0 | $ 13.0 | $ 6.0 | $ 12.0
Effective income tax rate reconciliation, uncertainty of taxes | 3.0 |  |  |
Unrecognized tax benefits that would have an impact on effective tax rate | 14.0 |  |  |
Unrecognized tax benefits that would have an impact on effective tax rate, net of tax | 13.0 |  |  |
General Business Tax Credit |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Tax credit carryovers | 1,022.0 |  |  |
Tax Year 2018 Through 2013 |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Operating loss carryback | 29.0 |  |  |
Net tax refund | 2.5 |  |  |
Tax Year 2013 |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Discrete income tax benefit | 4.0 |  |  |
State |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Operating loss carryforwards, valuation allowance | 18.0 |  |  |
State | New York State |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Operating loss carryforwards | 1,351.0 |  |  |
State | New York City |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Valuation allowance reversed | $ 9.0 |  |  |
Deferred tax asset, period of realization | 10 years |  |  |
CECONY |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Unrecognized Tax Benefits | $ 3.0 | $ 2.0 | $ 4.0 | $ 5.0
Effective income tax rate reconciliation, uncertainty of taxes | 1.0 |  |  |
Unrecognized tax benefits that would have an impact on effective tax rate | $ 3.0 |  |  |

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- Definition Carrying amount as of the balance sheet date of income taxes previously overpaid to tax authorities (such as U.S. Federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes. Also called income tax refund receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(8)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(10)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in income tax contingencies. Including, but not limited to, domestic tax contingency, foreign tax contingency, state and local tax contingency, and other contingencies. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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