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Changes in Accumulated Other Comprehensive Income Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Mar. 23, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Loss |  |  |  | $ (112) | $ 947 | $ 297
Income Tax Expense (Benefit) |  | $ 26 |  | 120 | (126) | 753
Net income (loss) |  |  |  | 2,084 | 3,876 | 1,196
Amortization of pension and other postretirement benefit plan items |  |  |  | 4 |  |
Amounts reclassified from AOCI | [1] |  |  | (182) | (144) |
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Income Tax Expense (Benefit) |  |  |  |  | (1) |
Gains and (Losses) on Cash Flow Hedges |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amounts reclassified from AOCI | [2],[3] |  |  | (1) | (4) |
Gains and (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Other cash flow hedges | [1] |  |  | (1) | (5) |
Total before tax | [1] |  |  | (1) | (5) |
Income Tax Expense (Benefit) | [1] |  |  | 0 | 1 |
Net of tax | [1] |  |  | (1) | (4) |
Prior service costs |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1],[4] |  |  | 90 | 92 |
Actuarial losses |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1],[4] |  |  | (333) | (324) |
Pension and Non-Pension Postretirement Benefit Plan Items |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1] |  |  | (243) | (232) |
Tax benefit | [1] |  |  | 62 | 92 |
Amounts reclassified from AOCI | [1],[2],[3] |  |  | (181) | (140) |
Exelon Generation Co L L C [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Loss |  |  |  | (178) | 948 | 401
Income Tax Expense (Benefit) |  |  |  | (108) | (1,376) | 282
Net income (loss) |  |  |  | 443 | 2,798 | $ 550
Amortization of pension and other postretirement benefit plan items |  |  |  | 3 |  |
Amounts reclassified from AOCI | [1] |  |  | (1) | (4) |
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amounts reclassified from AOCI | [2],[3] |  |  | (1) | (4) |
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Other cash flow hedges | [1] |  |  | (1) | (5) |
Total before tax | [1] |  |  | (1) | (5) |
Income Tax Expense (Benefit) | [1] |  |  | 0 | 1 |
Net of tax | [1] |  |  | (1) | (4) |
Exelon Generation Co L L C [Member] | Prior service costs |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1],[4] |  |  | 0 | 0 |
Exelon Generation Co L L C [Member] | Actuarial losses |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1],[4] |  |  | 0 | 0 |
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Amortization of pension and other postretirement benefit plan items | [1] |  |  | 0 | 0 |
Tax benefit | [1] |  |  | 0 | 0 |
Amounts reclassified from AOCI | [1],[2],[3] |  |  | 0 | 0 |
Pepco Holdings LLC [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Loss |  |  |  | 43 | 54 |
Income Tax Expense (Benefit) |  |  |  | 35 | 217 |
Net income (loss) |  |  |  | $ 398 | $ 362 |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Loss |  |  | $ (4) |  |  |
Income Tax Expense (Benefit) |  |  | 17 |  |  |
Net income (loss) |  |  | $ 19 |  |  |
[1] | Amounts in parenthesis represent a decrease in net income.
[2] | All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3] | See next tables for details about these reclassifications.
[4] | This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 16 — Retirement Benefits for additional information.

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