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Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($) | Dec. 31, 2018 | Dec. 31, 2017
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Spent Nuclear Fuel Obligation, Noncurrent | $ 1,171,000,000 | $ 1,147,000,000
Forward Power Basis | 3.18 |
Forward Gas Basis | 0.64 |
Exelon Generation Co L L C [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Spent Nuclear Fuel Obligation, Noncurrent | 1,171,000,000 | 1,147,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Spent Nuclear Fuel Obligation, Noncurrent | $ 119,000,000 | $ 114,000,000

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- Definition Basis adjustment to the forward gas price to deliver at an illiquid location + References No definition available. + Details
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- Definition Basis adjustment to the forward power price to deliver at an illiquid location. + References No definition available. + Details
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- Definition Provision for the disposal costs of spent nuclear fuel from generating stations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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