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Asset Retirement Obligations - Unrealized Gain on NDT Funds (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Asset Retirement Obligations [Line Items] |  |  |
Decommissioning Fund Investments | $ 11,661 | $ 13,272 |
Exelon Generation Co L L C [Member] |  |  |
Asset Retirement Obligations [Line Items] |  |  |
Decommissioning Fund Investments | 11,661 | 13,272 |
Collateral Pledged [Member] | Unregulated Operation [Member] | Exelon Generation Co L L C [Member] |  |  |
Asset Retirement Obligations [Line Items] |  |  |
Unrealized Gain (Loss) on Investments | (483) | 521 | $ 194
Collateral Pledged [Member] | Regulated Operation [Member] | Exelon Generation Co L L C [Member] |  |  |
Asset Retirement Obligations [Line Items] |  |  |
Unrealized Gain (Loss) on Investments | (715) | 455 | $ 216
Assets, Total [Member] |  |  |
Asset Retirement Obligations [Line Items] |  |  |
Decommissioning Fund Investments | $ 12,695 | $ 13,349 |

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- Definition Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period. + References Reference 1: 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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