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Early Plant Retirements Early Plant Retirements (Tables) | 12 Months Ended
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Dec. 31, 2018
Implications of Potential Early Plant Retirements [Abstract] |
Schedule of Other Operating Cost and Expense, by Component [Table Text Block] | The total annual impact of these charges by year are summarized in the table below.
Income statement expense (pre-tax) |  | 2018(a) |  | 2017(b) |  | 2016(c)
Depreciation and Amortization |  |  |  |  |  |
Accelerated depreciation(d) |  | $ | 539 |  |  | $ | 250 |  |  | $ | 712 |
Accelerated nuclear fuel amortization |  | 57 |  |  | 12 |  |  | 60 |
Operating and Maintenance |  |  |  |  |  |
One-time charges(e,f) |  | 32 |  |  | 77 |  |  | 26 |
Change in ARO accretion, net of any contractual offset(g) |  | — |  |  | — |  |  | 2 |
Contractual offset for ARC depreciation(g) |  | — |  |  | — |  |  | (86 | )
Total |  | $ | 628 |  |  | $ | 339 |  |  | $ | 714 |
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(a) | Reflects incremental accelerated depreciation for TMI and Oyster Creek. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 2018.
(b) | Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017.
(c) | Reflects incremental charges for Clinton and Quad Cities including incremental accelerated depreciation and amortization from June 2, 2016 through December 6, 2016. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation updated the expected economic useful life for both facilities, to 2027 for Clinton, commensurate with the end of the Illinois ZES, and to 2032 for Quad Cities, the end of its current operating license. Depreciation was therefore adjusted beginning December 7, 2016, to reflect these extended useful life estimates.
(d) | Reflects incremental accelerated depreciation of plant assets, including any ARC.
(e) | Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Excludes the charge to Operating and maintenance expense from the ARO remeasurement due to the announced sale of Oyster Creek. See Note 5 — Mergers, Acquisitions and Dispositions for additional information.
(f) | In June 2016, as a result of the retirement decision for Clinton and Quad Cities, Exelon and Generation recognized one-time charges of $146 million. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation reversed approximately $120 million of these one-time charges initially recorded in June 2016.
(g) | For Quad Cities based on the regulatory agreement with the ICC, decommissioning-related activities are offset within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The offset results in an equal adjustment to the noncurrent payables to ComEd at Generation and an adjustment to the regulatory liabilities at ComEd. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability.
Implications of Potential Early Plant Retirement on Balance Sheet [Table Text Block] | The following table provides the balance sheet amounts as of December 31, 2018 for Generation’s significant assets and liabilities associated with the Mystic Units 8 and 9 and Everett Marine Terminal assets that would potentially be impacted by a decision to permanently cease generation operations.
|  | December 31, 2018
Asset Balances |  |
Materials and supplies inventory |  | $ | 30 |
Fuel inventory |  | 20 |
Completed plant, net |  | 901 |
Construction work in progress |  | 9 |
Liability Balances |  |
Asset retirement obligation |  | (1 | )
|  | December 31, 2018
Asset Balances |  |
Materials and supplies inventory |  | $ | 45 |
Nuclear fuel inventory, net |  | 118 |
Completed plant, net |  | 538 |
Construction work in progress |  | 44 |
Liability Balances |  |
Asset retirement obligation |  | (395 | )
NRC License Renewal Term |  | 2036 (unit 1) |
|  | 2040 (unit 2) |

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- Definition Tabular disclosure of each detailed component of other operating costs and expenses that are applicable to sales and revenues, but not included in the cost of sales in the income statement. + 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 + Details
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