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Summary of Significant Accounting Policies and Other Matters - Plant and Depreciation (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Accumulated amortization | $ 126 | $ 29 |
Annual aggregate depreciation allowance | 1,417 |  |
Software Licenses |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Gross asset | 93 | 100 |
Estimated aggregate annual amortization expense | 7 |  |
Accumulated amortization | $ 10 | $ 3 |
Non-Utility Plant | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 10 years |  |
CECONY |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
AFUDC rates (percent) | 5.10% | 5.40% | 5.50%
Average depreciation rates (percent) | 3.20% | 3.10% | 3.10%
Annual aggregate depreciation allowance | $ 1,332 |  |
CECONY | Software Licenses |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Gross asset | 88 | $ 95 |
Estimated aggregate annual amortization expense | 7 |  |
Accumulated amortization | $ 0 | $ 3 |
CECONY | Electric | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
CECONY | Electric | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 95 years |  |
CECONY | Gas | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
CECONY | Gas | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 90 years |  |
CECONY | Steam | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
CECONY | Steam | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 80 years |  |
CECONY | General Plant | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
CECONY | General Plant | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 55 years |  |
O&R |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
AFUDC rates (percent) | 5.30% | 2.20% | 2.50%
Average depreciation rates (percent) | 3.00% | 2.90% | 2.90%
O&R | Electric | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
O&R | Electric | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 75 years |  |
O&R | Gas | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
O&R | Gas | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 75 years |  |
O&R | General Plant | Minimum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 5 years |  |
O&R | General Plant | Maximum |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives (years) | 50 years |  |

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