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Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | $ (12,533) | $ (12,490)
Deferred Tax Liabilities, Other Finite-Lived Assets | 117 | 150
Derivatives and other financial instruments | 89 | (85)
Deferred pension and postretirement obligation | 1,435 | 1,463
Deferred Tax Liabilities, Investments | (351) | (553)
Deferred debt refinancing costs | 234 | 217
Deferred Tax Liabilities, Regulatory Assets and Liabilities | (749) | (688)
Tax loss carryforward | 237 | 344
Tax credit carryforward | 811 | 861
Investment in partnerships | (797) | (434)
Other, net | 934 | 746
Deferred income tax liabilities (net) | (10,573) | (10,469)
Unamortized investment tax credits | (724) | (732)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (11,297) | (11,201)
Exelon Generation Co L L C [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (2,495) | (2,819)
Deferred Tax Liabilities, Other Finite-Lived Assets | (44) | (66)
Derivatives and other financial instruments | 35 | (66)
Deferred pension and postretirement obligation | (188) | (205)
Deferred Tax Liabilities, Investments | (351) | (553)
Deferred debt refinancing costs | 23 | 26
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 0 | 0
Tax loss carryforward | 78 | 76
Tax credit carryforward | 816 | 868
Investment in partnerships | (775) | (416)
Other, net | 239 | 78
Deferred income tax liabilities (net) | (2,662) | (3,077)
Unamortized investment tax credits | (700) | (705)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (3,362) | (3,782)
Commonwealth Edison Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (4,059) | (3,825)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 69 | (2)
Deferred pension and postretirement obligation | (255) | (285)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | (7) | (8)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 300 | 489
Tax loss carryforward | 0 | 33
Tax credit carryforward | 0 | 1
Investment in partnerships | 0 | 0
Other, net | 151 | 141
Deferred income tax liabilities (net) | (3,801) | (3,456)
Unamortized investment tax credits | (12) | (13)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (3,813) | (3,469)
PECO Energy Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (1,862) | (1,762)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 0 | 0
Deferred pension and postretirement obligation | (26) | (15)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | 0 | (1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | (129) | (90)
Tax loss carryforward | 18 | 9
Tax credit carryforward | 0 | 0
Investment in partnerships | 0 | 0
Other, net | 67 | 71
Deferred income tax liabilities (net) | (1,932) | (1,788)
Unamortized investment tax credits | (1) | (1)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (1,933) | (1,789)
Baltimore Gas and Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (1,399) | (1,368)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 0 | 0
Deferred pension and postretirement obligation | (26) | (29)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | (3) | (3)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 172 | 136
Tax loss carryforward | 25 | 11
Tax credit carryforward | 0 | 0
Investment in partnerships | 0 | 0
Other, net | 12 | 13
Deferred income tax liabilities (net) | (1,219) | (1,240)
Unamortized investment tax credits | (3) | (4)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (1,222) | (1,244)
Pepco Holdings LLC [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (2,577) | (2,521)
Deferred Tax Liabilities, Other Finite-Lived Assets | 161 | 216
Derivatives and other financial instruments | 3 | 3
Deferred pension and postretirement obligation | (102) | (130)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | 187 | 203
Deferred Tax Liabilities, Regulatory Assets and Liabilities | (90) | (184)
Tax loss carryforward | 96 | 156
Tax credit carryforward | 0 | 6
Investment in partnerships | 0 | 0
Other, net | 196 | 193
Deferred income tax liabilities (net) | (2,126) | (2,058)
Unamortized investment tax credits | (8) | (8)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (2,134) | (2,066)
Atlantic City Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (645) | (607)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 0 | 0
Deferred pension and postretirement obligation | (14) | (18)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | (1) | (1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 83 | 86
Tax loss carryforward | 26 | 35
Tax credit carryforward | 0 | 0
Investment in partnerships | 0 | 0
Other, net | 19 | 16
Deferred income tax liabilities (net) | (532) | (489)
Unamortized investment tax credits | (3) | (4)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (535) | (493)
Delmarva Power & Light Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (743) | (717)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 0 | 0
Deferred pension and postretirement obligation | (46) | (51)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | (2) | (2)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 96 | 88
Tax loss carryforward | 52 | 68
Tax credit carryforward | 0 | 0
Investment in partnerships | 0 | 0
Other, net | 17 | 14
Deferred income tax liabilities (net) | (626) | (600)
Unamortized investment tax credits | (2) | (3)
Total deferred income tax liabilities (net) and unamortized investment tax credits | (628) | (603)
Potomac Electric Power Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Plant basis differences | (1,148) | (1,152)
Deferred Tax Liabilities, Other Finite-Lived Assets | 0 | 0
Derivatives and other financial instruments | 0 | 0
Deferred pension and postretirement obligation | (78) | (78)
Deferred Tax Liabilities, Investments | 0 | 0
Deferred debt refinancing costs | (4) | (4)
Deferred Tax Liabilities, Regulatory Assets and Liabilities | 58 | 39
Tax loss carryforward | 12 | 40
Tax credit carryforward | 0 | 0
Investment in partnerships | 0 | 0
Other, net | 98 | 94
Deferred income tax liabilities (net) | (1,062) | (1,061)
Unamortized investment tax credits | (2) | (2)
Total deferred income tax liabilities (net) and unamortized investment tax credits | $ (1,064) | $ (1,063)

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