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Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 | Mar. 23, 2016 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes | $ 26 |  |  | $ 120 | $ (126) | $ 753
Exelon Generation Co L L C [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | (108) | (1,376) | 282
Commonwealth Edison Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 168 | 417 | 301
PECO Energy Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 6 | 104 | 149
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 74 | 218 | 174
Potomac Electric Power Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 13 | 105 | 41
Delmarva Power & Light Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 22 | 71 | 22
Atlantic City Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 12 | 26 | (4)
Pepco Holdings LLC [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  |  | 35 | 217 |
Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  |  | $ 3 |  |  |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Income taxes |  | $ 17 |  |  |  |
Internal Revenue Service (IRS) [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 226 | 194 | 60
Deferred |  |  |  | (98) | (471) | 600
Investment Tax Credit |  |  |  | (24) | (25) | (24)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 337 | 584 | 513
Deferred |  |  |  | (347) | (2,005) | (254)
Investment Tax Credit |  |  |  | (21) | (21) | (20)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (63) | (191) | (135)
Deferred |  |  |  | 145 | 523 | 379
Investment Tax Credit |  |  |  | (2) | (2) | (2)
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 11 | 71 | 63
Deferred |  |  |  | 10 | 28 | 72
Investment Tax Credit |  |  |  | 0 | 0 | 0
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (5) | 74 | 51
Deferred |  |  |  | 47 | 101 | 88
Investment Tax Credit |  |  |  | 0 | (1) | (1)
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 28 | (20) | (118)
Deferred |  |  |  | (21) | 114 | 136
Investment Tax Credit |  |  |  | 0 | 0 | 0
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (3) | (24) | (88)
Deferred |  |  |  | 13 | 82 | 97
Investment Tax Credit |  |  |  | 0 | 0 | 0
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (14) | (12) | (26)
Deferred |  |  |  | 18 | 34 | 22
Investment Tax Credit |  |  |  | 0 | 0 | 0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (4) | (60) |
Deferred |  |  |  | 24 | 250 |
Investment Tax Credit |  |  |  | (1) | (1) |
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  | (281) |  |  |
Deferred |  |  | 283 |  |  |
Investment Tax Credit |  |  | (1) |  |  |
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  | 0 |  |  |  |
Deferred |  | 10 |  |  |  |
Investment Tax Credit |  | 0 |  |  |  |
State and Local Jurisdiction [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (1) | 14 | 39
Deferred |  |  |  | 17 | 162 | 78
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 6 | 65 | 45
Deferred |  |  |  | (83) | 1 | (2)
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | (29) | (49) | (4)
Deferred |  |  |  | 117 | 136 | 63
State and Local Jurisdiction [Member] | PECO Energy Co [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 1 | 14 | 9
Deferred |  |  |  | (16) | (9) | 5
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 0 | (5) | 5
Deferred |  |  |  | 32 | 49 | 31
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 0 | (2) | 7
Deferred |  |  |  | 6 | 13 | 16
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 0 | 0 | 1
Deferred |  |  |  | 12 | 13 | 12
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 0 | 0 | 0
Deferred |  |  |  | 8 | 4 | $ 0
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  |  | 7 | (4) |
Deferred |  |  |  | $ 9 | $ 32 |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  |  | (11) |  |  |
Deferred |  |  | $ 13 |  |  |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Current |  | 0 |  |  |  |
Deferred |  | $ 7 |  |  |  |

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