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Supplemental Financial Information Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 23, 2016 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Net realized income on NDT funds - Regulatory agreement units | [1] |  |  | $ 506 | $ 488 | $ 237
Net realized income on NDT funds - Non-regulatory agreement units | [1] |  |  | 302 | 209 | 126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units |  |  |  | (715) | 455 | 216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement |  |  |  | (483) | 521 | 194
Net unrealized income (losses) on pledged assets |  |  |  | (8) | (10) | (1)
Regulatory offset to NDT fund-related activities | [2] |  |  | 171 | (724) | (372)
Total decommissioning-related activities |  |  |  | (227) | 939 | 400
Investment income (loss) |  |  |  | 43 | 8 | 17
Long-term lease income |  |  |  |  |  | 4
Interest income (expense) related to uncertain income tax positions |  |  |  | 5 | 3 | 13
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 2 | (106)
AFUDC—Equity |  |  |  | 69 | 73 | 64
Non-service net periodic benefit cost |  |  |  | (47) | (109) | (116)
Loss on debt extinguishment |  |  |  |  |  | (3)
Other |  |  |  | 45 | 31 | 24
Other, net |  |  |  | (112) | 947 | 297
Exelon Generation Co L L C [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Net realized income on NDT funds - Regulatory agreement units | [1] |  |  | 506 | 488 | 237
Net realized income on NDT funds - Non-regulatory agreement units | [1] |  |  | 302 | 209 | 126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units |  |  |  | (715) | 455 | 216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement |  |  |  | (483) | 521 | 194
Net unrealized income (losses) on pledged assets |  |  |  | (8) | (10) | (1)
Regulatory offset to NDT fund-related activities | [2] |  |  | 171 | (724) | (372)
Total decommissioning-related activities |  |  |  | (227) | 939 | 400
Investment income (loss) |  |  |  | 32 | 6 | 8
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 1 | (1) | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 0 | 0 | 0
Loss on debt extinguishment |  |  |  |  |  | (2)
Other |  |  |  | 16 | 4 | (5)
Other, net |  |  |  | (178) | 948 | 401
Commonwealth Edison Co [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 0 | 0 | 0
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | (86)
AFUDC—Equity |  |  |  | 19 | 12 | 14
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 14 | 10 | 7
Other, net |  |  |  | 33 | 22 | (65)
PECO Energy Co [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 1 | 0 | (1)
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 7 | 9 | 8
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 0 | 0 | 1
Other, net |  |  |  | 8 | 9 | 8
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 1 | 0 | 2
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 18 | 16 | 19
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 0 | 0 | 0
Other, net |  |  |  | 19 | 16 | 21
Pepco Holdings LLC [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 4 | 2 |
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 |
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 |
AFUDC—Equity |  |  |  | 25 | 36 |
Other |  |  |  | 14 | 16 |
Other, net |  |  |  | 43 | 54 |
Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  | $ 1 |  |  |
Long-term lease income |  |  | 0 |  |  |
Interest income (expense) related to uncertain income tax positions |  |  | (1) |  |  |
Benefit (penalty) related to uncertain income tax positions | [3] |  | 0 |  |  |
AFUDC—Equity |  |  | 23 |  |  |
Loss on debt extinguishment |  |  | 0 |  |  |
Other |  |  | 21 |  |  |
Other, net |  |  | $ 44 |  |  |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  | $ 0 |  |  |  |
Long-term lease income |  | 0 |  |  |  |
Interest income (expense) related to uncertain income tax positions |  | 0 |  |  |  |
Benefit (penalty) related to uncertain income tax positions | [3] | 0 |  |  |  |
AFUDC—Equity |  | 7 |  |  |  |
Loss on debt extinguishment |  | 0 |  |  |  |
Other |  | (11) |  |  |  |
Other, net |  | $ (4) |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 2 | 1 | 1
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 1
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 22 | 23 | 19
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 7 | 8 | 15
Other, net |  |  |  | 31 | 32 | 36
Delmarva Power & Light Company [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 1 | 0 | 0
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 2 | 7 | 5
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 7 | 7 | 8
Other, net |  |  |  | 10 | 14 | 13
Atlantic City Electric Company [Member] |  |  |  |  |  |
Decommissioning-Related Activities [Abstract] |  |  |  |  |  |
Investment income (loss) |  |  |  | 0 | 0 | 1
Long-term lease income |  |  |  |  |  | 0
Interest income (expense) related to uncertain income tax positions |  |  |  | 0 | 0 | 0
Benefit (penalty) related to uncertain income tax positions | [3] |  |  |  | 0 | 0
AFUDC—Equity |  |  |  | 1 | 6 | 6
Loss on debt extinguishment |  |  |  |  |  | 0
Other |  |  |  | 1 | 1 | 2
Other, net |  |  |  | $ 2 | $ 7 | $ 9
[1] | Includes investment income and realized gains and losses on sales of investments within the NDT funds.
[2] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MTE0OEY2QkJBNTBGNUFBQ0IwMkE4RTI0QzY3MTNDRUEM}
[3] | See Note 14—Income Taxes for additional information on the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position.

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- Definition This item represents investment income and realized gains (losses) for the period as a result of selling marketable securities held in nuclear decommissioning trust funds and classified as trading securities. As a result of certain regulatory agreements for these nuclear decommissioning trust funds; upon completion of decommissioning activities, excess (shortfall of) funds will be refunded to (recovered from) rate payers through a regulated affiliate. Therefore, this activity is contractually eliminated within the income statement. + References No definition available. + Details
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- Definition This item represents the contractual elimination of nuclear decommissioning trust fund-related activity, which may include realized income (losses), unrealized income (losses), asset retirement obligation accretion, asset retirement cost amortization, investment income and related income taxes. As a result of certain regulatory agreements for these nuclear decommissioning trust funds; upon completion of decommissioning activities, excess (shortfall of) funds will be refunded to (recovered from) rate payers through a regulated affiliate. Therefore, this activity is contractually eliminated within the income statement. + References No definition available. + Details
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