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Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions | Dec. 31, 2018 USD ($)
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Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | $ 811 | [1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 816 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Potomac Electric Power Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Delmarva Power & Light Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Atlantic City Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Federal general business credits carryforwards | 0 |
State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 4,103 | [2]
Deferred taxes on state tax attributes (net) | 272 |
Valuation allowance on state tax attributes | 35 |
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 1,544 | [2]
Deferred taxes on state tax attributes (net) | 104 |
Valuation allowance on state tax attributes | 26 |
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 0 |
Deferred taxes on state tax attributes (net) | 0 |
Valuation allowance on state tax attributes | 0 |
State and Local Jurisdiction [Member] | PECO Energy Co [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 224 | [3]
Deferred taxes on state tax attributes (net) | 18 |
Valuation allowance on state tax attributes | 0 |
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 395 | [4]
Deferred taxes on state tax attributes (net) | 26 |
Valuation allowance on state tax attributes | 1 |
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 1,492 | [5]
Deferred taxes on state tax attributes (net) | 102 |
Valuation allowance on state tax attributes | 6 |
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 192 | [6]
Deferred taxes on state tax attributes (net) | 12 |
Valuation allowance on state tax attributes | 0 |
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 772 | [7]
Deferred taxes on state tax attributes (net) | 52 |
Valuation allowance on state tax attributes | 0 |
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
State net operating losses | 365 | [8]
Deferred taxes on state tax attributes (net) | 26 |
Valuation allowance on state tax attributes | $ 0 |
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[2] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MDkyRDA3MDExQ0UwNUM3Q0JGMTJENTVGQjRDRkUxMEUM}
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[4] | .
[5] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246RjE3NUQ0OEVCOEU4NTZBNjhDMkY3MzUwQUY0NTc3MDAM}
[6] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NzBCNTFENTBCREJGNTIxMzhFRURCRkZFQzYxRDA1MDMM}
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[8] | .

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- Definition The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 30 -Paragraph 5 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=75018887&loc=d3e30536-109315 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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