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Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Mar. 24, 2016
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible asset amortization expense |  | $ (109) | $ (237) | $ (336) |
Potomac Electric Power Company [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fresh-Start Adjustment, Increase (Decrease), Goodwill |  |  |  |  | $ 400
Exelon Generation Co L L C [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible asset amortization expense |  | 63 | 83 | 79 |
Commonwealth Edison Co [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible asset amortization expense |  | 7 | 7 | 7 |
PHI Service Co Affiliate [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible asset amortization expense |  | (188) | (336) | (430) |
Delmarva Power & Light Company [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fresh-Start Adjustment, Increase (Decrease), Goodwill |  |  |  |  | $ 300
Unamortized Energy Contracts [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Amortization of Power Contracts Emission Credits | [1] | 14 | 35 | 35 |
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Amortization of Power Contracts Emission Credits | [1] | $ 14 | $ 35 | $ 35 |
[1] | Included in Operating revenues or Purchased power and fuel in the Registrants’ Consolidated Statements of Operations and Comprehensive Income

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition The expense charged against earnings for the periodic recognition of capitalized costs related to purchasing power, fuel, or emission credits. These items may be purchased in one accounting period but are deducted from earnings over time through amortization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition Amount of fresh-start adjustment to goodwill. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6918054&loc=SL2890621-112765 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 45 -Paragraph 20 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=64805424&loc=SL2890583-112764 + Details
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