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Summary of Significant Accounting Policies and Other Matters - Utility Plant (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items] |  |
Accumulated amortization | $ 254 | $ 228
Other deferred charges and noncurrent assets | 57 | 54
Prepayments | 14 | 12
Depreciation expense | 3 |
Accumulated depreciation | 12 | 10
Software Licenses |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross asset | 84 | 86
Estimated aggregate annual amortization expense | 7 |
Accumulated amortization | 19 | 17
CECONY |  |
Finite-Lived Intangible Assets [Line Items] |  |
Other deferred charges and noncurrent assets | 54 | 51
Prepayments | 13 | 11
Depreciation expense | 3 |
Accumulated depreciation | 11 | 8
CECONY | Software Licenses |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross asset | 80 | 81
Estimated aggregate annual amortization expense | 7 |
Accumulated amortization | $ 18 | $ 17

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