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Income Taxes - Narrative (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jul. 27, 2018 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 23, 2016 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 1999
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  | $ 71 |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Limitation on Deductible Interest Expense |  |  |  |  |  |  |  |  | 100.00% |  |  |  |
Allowable Expensing For Cost Of Qualified Property |  |  |  |  |  |  |  |  | 30.00% |  |  |  |
Unrecognized Tax Benefits |  |  | $ 477 |  |  |  | $ 916 | $ 477 | $ 743 | $ 916 |  | $ 1,078 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | (2) | 106 |  |  |
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities |  | 9 |  |  |  |  |  |  |  |  |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  | 90 | 241 |  |  |  |  | 241 |  |  |  |  |
Income taxes |  |  | 26 |  |  |  |  | 120 | (126) | 753 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (251) | (196) | (21) |  |  |
Taxes accrued |  |  | 412 |  |  |  |  | 412 | 373 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | (17) |  |  |  |  | (17) | (17) |  |  |  |
Tax positions for which there is uncertainty about the timing of tax benefits |  |  |  |  |  |  | 83 |  | 7 | 83 |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  | $ 20 | 463 |  |  |  | 633 | 463 | 523 | $ 633 |  |  |
Regulatory Liabilities |  |  | 10,203 |  |  |  |  | 10,203 | 10,388 |  |  |  |
Regulatory Assets |  |  | 9,459 |  |  |  |  | 9,459 | $ 9,288 |  |  |  |
Like kind exchange [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred gain on sale of property |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,200
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | $ 90 |  |  |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  |  | $ 33 |  |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Unrecognized Tax Benefits |  |  | 408 |  |  |  | 490 | $ 408 | $ 468 | $ 490 |  | 534 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 33 |  |  |  |  | 33 |  |  |  |  |
Income taxes |  |  |  |  |  |  |  | (108) | (1,376) | 282 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (36) | (17) | (20) |  |  |
Taxes accrued |  |  | 226 |  |  |  |  | 226 | 444 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Tax positions for which there is uncertainty about the timing of tax benefits |  |  |  |  |  |  | 7 |  |  | 7 |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  | 408 |  |  |  | 483 | 408 | 461 | 483 |  |  |
Allocation of federal tax benefit under tax sharing agreement |  |  | 155 |  |  |  | 94 | $ 155 | $ 102 | $ 94 |  |  |
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Unrecognized Tax Benefits |  |  | 2 |  |  |  | (12) | $ 2 | $ 2 | $ (12) |  | 142 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 86 |  |  |
Income taxes |  |  |  |  |  |  |  | 168 | 417 | 301 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Taxes accrued |  |  | 71 |  |  |  |  | 71 | 60 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Tax positions for which there is uncertainty about the timing of tax benefits |  |  |  |  |  |  | (12) |  |  | $ (12) |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  | 2 |  |  |  |  | 2 | 2 |  |  |  |
Allocation of federal tax benefit under tax sharing agreement |  |  | 1 |  |  |  |  | 1 |  |  |  |  |
Regulatory Liabilities |  |  | 6,343 |  |  |  |  | $ 6,343 | 6,577 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | $ 1,279 |  |  |  |
Commonwealth Edison Co [Member] | Like kind exchange [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  |  | 2 |  |  |  |  |  |  |  |  |
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Unrecognized Tax Benefits |  |  | 0 |  |  |  | 0 | $ 0 | $ 0 | $ 0 |  | 0 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Income taxes |  |  |  |  |  |  |  | 6 | 104 | 149 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Taxes accrued |  |  | 28 |  |  |  |  | 28 | 15 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Allocation of federal tax benefit under tax sharing agreement |  |  | 48 |  |  |  | 18 | 48 | 16 | 18 |  |  |
Regulatory Liabilities |  |  | 596 |  |  |  |  | $ 596 | 690 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 410 |  |  |  |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  |  |  |  |  |  | 120 |  | $ 120 | $ 120 |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Unrecognized Tax Benefits |  |  | 0 |  |  |  | 120 | $ 0 | $ 120 | $ 120 |  | 120 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 120 |  |  |  |  | 120 |  |  |  |  |
Income taxes |  |  |  |  |  |  |  | 74 | 218 | 174 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (120) | 0 | 0 |  |  |
Taxes accrued |  |  | 46 |  |  |  |  | 46 | 71 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Allocation of federal tax benefit under tax sharing agreement |  |  | 26 |  |  |  | 8 | 26 | 10 | 8 |  |  |
Regulatory Liabilities |  |  | 1,269 |  |  |  |  | $ 1,269 | 1,163 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 571 |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  |  |  |  |  |  | 59 |  | $ 59 | $ 59 |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |  |
Unrecognized Tax Benefits |  |  | 0 |  |  |  | 80 | $ 0 | $ 59 | $ 80 |  | 8 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 66 |  |  |  |  | 66 |  |  |  |  |
Income taxes |  |  |  |  |  |  |  | 13 | 105 | 41 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (66) | (21) | 0 |  |  |
Taxes accrued |  |  | 58 |  |  |  |  | 58 | 68 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  |  |  |  |  | 21 |  |  | 21 |  |  |
Regulatory Liabilities |  |  | 829 |  |  |  |  | $ 829 | 832 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 891 |  |  |  |
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  |  |  |  |  |  | 21 |  | $ 21 | $ 21 |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% | [1] |  |
Unrecognized Tax Benefits |  |  | 0 |  |  |  | 37 | $ 0 | $ 21 | $ 37 |  | 3 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 22 |  |  |  |  | 22 |  |  |  |  |
Income taxes |  |  |  |  |  |  |  | 22 | 71 | 22 |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (22) | (16) | 0 |  |  |
Taxes accrued |  |  | 4 |  |  |  |  | 4 | 4 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  |  |  |  |  | 16 |  |  | $ 16 |  |  |
Regulatory Liabilities |  |  | 665 |  |  |  |  | $ 665 | 635 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 314 |  |  |  |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  |  |  |  |  |  |  |  | $ 14 |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% | [1] |  |
Unrecognized Tax Benefits |  |  | 14 |  |  |  | 22 | $ 14 | $ 14 | $ 22 |  | 0 |
Unrecognized Tax Benefits, Income Tax Penalties Expense |  |  |  |  |  |  |  | 0 | 0 | 0 |  |  |
Income taxes |  |  |  |  |  |  |  | 12 | 26 | (4) |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | 0 | (22) | 0 |  |  |
Taxes accrued |  |  | 5 |  |  |  |  | 5 | 5 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  |  |  |  |  | 22 |  |  | 22 |  |  |
Regulatory Liabilities |  |  | 420 |  |  |  |  | $ 420 | 422 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 430 |  |  |  |
Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in Unrecognized Tax Benefits is Reasonably Possible |  |  |  |  |  |  | 80 |  | $ 94 | 80 |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  | 21.00% | 35.00% |  |  |  |
Unrecognized Tax Benefits |  |  | 45 |  |  |  | $ 172 | $ 45 | $ 125 | 172 |  |  |
Income taxes |  |  |  |  |  |  |  | 35 | 217 |  |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  | (88) | (61) |  |  |  |
Taxes accrued |  |  | 74 |  |  |  |  | 74 | 61 |  |  |  |
Unrecognized Tax Benefits, Income Tax Penalties Accrued |  |  | 0 |  |  |  |  | 0 | 0 |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  |  |  |  |  |  |  | 32 |  |  |  |
Allocation of federal tax benefit under tax sharing agreement |  |  | 2 |  |  |  |  | 2 | 7 |  |  |  |
Regulatory Liabilities |  |  | 1,948 |  |  |  |  | 1,948 | 1,928 |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 3,047 |  |  |  |
Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent | [1] |  |  |  |  |  | 35.00% |  |  |  |  |  |
Income taxes |  |  |  |  |  |  | $ 3 |  |  |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  | 31 |  |  |  | 93 | 31 |  | 93 |  |  |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  | 35.00% |  |  |  |  |  |  |
Unrecognized Tax Benefits |  |  |  |  |  |  | 172 |  |  | 172 |  | $ 22 |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 88 |  |  |  |  | 88 |  |  |  |  |
Income taxes |  |  |  |  |  | $ 17 |  |  |  |  |  |  |
Unrecognized Tax Benefits, Period Increase (Decrease) |  |  |  |  |  |  |  |  |  | 0 |  |  |
Internal Revenue Service (IRS) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | (98) | (471) | 600 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 146 |  |  |  |
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | (347) | (2,005) | (254) |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 19 |  |  |  |
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 145 | 523 | 379 |  |  |
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 10 | 28 | 72 |  |  |
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 47 | 101 | 88 |  |  |
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | (21) | 114 | 136 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 21 |  |  |  |
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 13 | 82 | 97 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 16 |  |  |  |
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 18 | 34 | 22 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 22 |  |  |  |
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 24 | 250 |  |  |  |
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  | 283 |  |  |  |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  |  |  |  |  |  |  | 59 |  |  |  |
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  | 10 |  |  |  |  |  |  |
State and Local Jurisdiction [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 17 | 162 | 78 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  | 425 |  |  |  |  | 425 |  |  |  |  |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate |  |  | 411 |  |  |  |  | 411 |  |  |  |  |
Increase (Decrease) in Deferred Income Taxes |  |  |  | 50 | $ 16 |  |  |  |  |  |  |  |
Increase (Decrease) in Income Taxes |  |  |  | 50 |  |  |  |  |  |  |  |  |
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | (83) | 1 | (2) |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  | 411 |  |  |  |  | 411 |  |  |  |  |
Increase (Decrease) in Deferred Income Taxes |  |  |  | 53 | 5 |  |  |  |  |  |  |  |
Increase (Decrease) in Income Taxes |  |  |  | 53 |  |  |  |  |  |  |  |  |
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 117 | 136 | 63 |  |  |
State and Local Jurisdiction [Member] | PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | (16) | (9) | 5 |  |  |
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 32 | 49 | 31 |  |  |
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 6 | 13 | 16 |  |  |
Increase (Decrease) in Deferred Income Taxes |  |  |  | 1 | 16 |  |  |  |  |  |  |  |
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 12 | 13 | 12 |  |  |
Increase (Decrease) in Deferred Income Taxes |  |  |  | 2 | 1 |  |  |  |  |  |  |  |
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 8 | 4 | $ 0 |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  | 14 |  |  |  |  | 14 |  |  |  |  |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | 14 |  |  |  |  | 14 |  |  |  |  |
Deferred |  |  |  |  |  |  |  | 9 | $ 32 |  |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit |  |  | 14 |  |  |  |  | 14 |  |  |  |  |
Increase (Decrease) in Deferred Income Taxes |  |  |  | 4 | $ 17 |  |  |  |  |  |  |  |
Increase (Decrease) in Income Taxes |  |  |  | 3 |  |  |  |  |  |  |  |  |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in Unrecognized Tax Benefits is Reasonably Possible |  |  | $ 21 |  |  |  |  | $ 21 |  |  |  |  |
Deferred |  |  |  |  |  |  | $ 13 |  |  |  |  |  |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred |  |  |  |  |  | $ 7 |  |  |  |  |  |  |
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities |  |  |  | 1 |  |  |  |  |  |  |  |  |
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities |  |  |  | 2 |  |  |  |  |  |  |  |  |
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities |  |  |  | 1 |  |  |  |  |  |  |  |  |
Net Regulatory Assets Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  | $ 1 |  |  |  |  |  |  |  |  |
[1] | DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016, and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016. As a result, positive percentages represent an income tax benefit for the periods presented.

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