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Other Postretirement Benefits - Additional Information (Details) - Other Postretirement Benefits - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |
Increase (decrease) in liability for other postretirement benefits | $ (21) | $ 102 |
Increase (decrease) in regulatory liabilities | $ 36 |  |
Health care cost trend rate for net periodic benefit cost, current | 5.20% | 5.40% | 5.60%
Health care cost trend rate for net periodic benefit cost | 4.50% |  |
Health care cost trend rate for benefit obligations, current | 7.04% | 5.20% | 5.40%
Health care cost trend rate for benefit obligations | 4.50% |  |
Expected contributions | $ 6 |  |
Clean Energy Businesses, Con Edison Transmission and RECO |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Credit to OCI (net of taxes) for unrecognized net losses | 2 |  |
CECONY |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Increase (decrease) in liability for other postretirement benefits | (13) | $ 128 |
Increase (decrease) in regulatory liabilities | 33 |  |
Expected contributions | $ 3 |  |

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