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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of Asset Retirement Obligations by Category | The following table presents the AROs recorded on the Consolidated Balance Sheets.
| December 31, 2020
|  |  | Duke |  |  |  | Duke |  | Duke |  | Duke |  | Duke |  |
| Duke |  | Energy |  | Progress |  | Energy |  | Energy |  | Energy |  | Energy |  |
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida |  | Ohio |  | Indiana |  | Piedmont
Decommissioning of nuclear power facilities(a) | $ | 6,845 |  |  | $ | 2,695 |  |  | $ | 4,101 |  |  | $ | 3,642 |  |  | $ | 459 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Closure of ash impoundments | 5,778 |  |  | 2,597 |  |  | 1,973 |  |  | 1,950 |  |  | 23 |  |  | 67 |  |  | 1,140 |  |  | — |
Other | 381 |  |  | 58 |  |  | 75 |  |  | 43 |  |  | 32 |  |  | 44 |  |  | 36 |  |  | 20 |
Total asset retirement obligation | $ | 13,004 |  |  | $ | 5,350 |  |  | $ | 6,149 |  |  | $ | 5,635 |  |  | $ | 514 |  |  | $ | 111 |  |  | $ | 1,176 |  |  | $ | 20 |
Less: Current portion | 718 |  |  | 264 |  |  | 283 |  |  | 283 |  |  | — |  |  | 3 |  |  | 168 |  |  | — |
Total noncurrent asset retirement obligation | $ | 12,286 |  |  | $ | 5,086 |  |  | $ | 5,866 |  |  | $ | 5,352 |  |  | $ | 514 |  |  | $ | 108 |  |  | $ | 1,008 |  |  | $ | 20 |
(a) Duke Energy amount includes purchase accounting adjustments related to the merger with Progress Energy.
Public Utilities General Disclosures | The following table summarizes information about the most recent site-specific nuclear decommissioning cost studies. Decommissioning costs are stated in 2018 or 2019 dollars, depending on the year of the cost study, and include costs to decommission plant components not subject to radioactive contamination.
| Annual Funding |  | Decommissioning |  |
(in millions) | Requirement(a) |  | Costs(a) |  | Year of Cost Study
Duke Energy | $ | 27 |  |  | $ | 9,105 |  |  | 2018 or 2019
Duke Energy Carolinas(b)(c) | — |  |  | 4,365 |  |  | 2018
Duke Energy Progress(d) | 27 |  |  | 4,181 |  |  | 2019
Duke Energy Florida(e) | — |  |  | 559 |  |  | N/A
(a) Amounts for Progress Energy equal the sum of Duke Energy Progress and Duke Energy Florida. (b) Decommissioning cost for Duke Energy Carolinas reflects its ownership interest in jointly owned reactors. Other joint owners are responsible for decommissioning costs related to their interest in the reactors. (c) Duke Energy Carolinas' site-specific nuclear decommissioning cost study completed in 2018 was filed with the NCUC and PSCSC in 2019. A new funding study was also completed and filed with the NCUC and PSCSC in 2019. (d) Duke Energy Progress' site-specific nuclear decommissioning cost study completed in 2019 was filed with the NCUC and PSCSC in March 2020. Duke Energy Progress also completed a funding study, which was filed with the NCUC and PSCSC in July 2020. (e) During 2019, Duke Energy Florida reached an agreement to transfer decommissioning work for Crystal River Unit 3 to a third party and decommissioning costs are based on the agreement with this third party rather than a cost study. Regulatory approval was received from the NRC and the FPSC in April 2020 and August 2020, respectively. See Note 3 for more information. The following table presents the fair value of NDTF assets legally restricted for purposes of settling AROs associated with nuclear decommissioning. Duke Energy Florida entered into an agreement with a third party to decommission Crystal River Unit 3 and was granted an exemption from the NRC, which allows for use of the NDTF for all aspects of nuclear decommissioning. The entire balance of Duke Energy Florida's NDTF may be applied toward license termination, spent fuel and site restoration costs incurred to decommission Crystal River Unit 3 and is excluded from the table below. See Note 16 for additional information related to the fair value of the Duke Energy Registrants' NDTFs.
| December 31,
(in millions) | 2020 |  | 2019
Duke Energy | $ | 7,726 |  |  | $ | 6,766 |
Duke Energy Carolinas | 4,381 |  |  | 3,837 |
Duke Energy Progress | 3,345 |  |  | 2,929 |
The following table includes the current expiration of nuclear operating licenses.
Unit | Year of Expiration
Duke Energy Carolinas |
Catawba Units 1 and 2 | 2043
McGuire Unit 1 | 2041
McGuire Unit 2 | 2043
Oconee Units 1 and 2 | 2033
Oconee Unit 3 | 2034
Duke Energy Progress |
Brunswick Unit 1 | 2036
Brunswick Unit 2 | 2034
Harris | 2046
Robinson | 2030
Rollforward Schedule of Asset Retirement Obligations | The following tables present changes in the liability associated with AROs.
|  |  | Duke |  |  |  | Duke |  | Duke |  | Duke |  | Duke |  |
| Duke |  | Energy |  | Progress |  | Energy |  | Energy |  | Energy |  | Energy |  |
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida |  | Ohio |  | Indiana |  | Piedmont
Balance at December 31, 2018 | $ | 10,467 |  |  | $ | 3,949 |  |  | $ | 5,411 |  |  | $ | 4,820 |  |  | $ | 591 |  |  | $ | 93 |  |  | $ | 722 |  |  | $ | 19 |
Accretion expense(a) | 508 |  |  | 235 |  |  | 252 |  |  | 227 |  |  | 25 |  |  | 3 |  |  | 28 |  |  | 1 |
Liabilities settled(b) | (895) |  |  | (329) |  |  | (499) |  |  | (460) |  |  | (39) |  |  | (12) |  |  | (54) |  |  | — |
Liabilities incurred in the current year | 25 |  |  | 18 |  |  | 7 |  |  | — |  |  | 7 |  |  | — |  |  | — |  |  | — |
Revisions in estimates of cash flows(c) | 3,213 |  |  | 1,861 |  |  | 1,300 |  |  | 1,306 |  |  | (6) |  |  | (4) |  |  | 136 |  |  | (3) |
Balance at December 31, 2019 | 13,318 |  |  | 5,734 |  |  | 6,471 |  |  | 5,893 |  |  | 578 |  |  | 80 |  |  | 832 |  |  | 17 |
Accretion expense(a) | 542 |  |  | 258 |  |  | 246 |  |  | 225 |  |  | 21 |  |  | 4 |  |  | 33 |  |  | 1 |
Liabilities settled(b) | (724) |  |  | (198) |  |  | (451) |  |  | (358) |  |  | (93) |  |  | (2) |  |  | (74) |  |  | — |
Liabilities incurred in the current year | 22 |  |  | — |  |  | 5 |  |  | — |  |  | 5 |  |  | — |  |  | — |  |  | — |
Revisions in estimates of cash flows(d) | (154) |  |  | (444) |  |  | (122) |  |  | (125) |  |  | 3 |  |  | 29 |  |  | 385 |  |  | 2 |
Balance at December 31, 2020 | $ | 13,004 |  |  | $ | 5,350 |  |  | $ | 6,149 |  |  | $ | 5,635 |  |  | $ | 514 |  |  | $ | 111 |  |  | $ | 1,176 |  |  | $ | 20 |
(a) Substantially all accretion expense for the years ended December 31, 2020, and 2019, relates to Duke Energy’s regulated operations and has been deferred in accordance with regulatory accounting treatment. (b) Amounts primarily relate to ash impoundment closures and nuclear decommissioning. (c) Amounts primarily relate to increases in closure estimates for certain ash impoundments as a result of the NCDEQ's April 1, 2019, Order and the related settlement agreement dated December 31, 2019. (d) Primarily relates to decreases due to revised basin closure cost estimates, partially offset by increases related to new closure plan approvals, post closure maintenance and beneficiation costs. Duke Energy Indiana estimates also include the impacts of closure estimates for certain ash impoundments due to the impact of Hoosier Environmental Council’s petition filed with the court challenging the Indiana Department of Environmental Management’s partial approval of Duke Energy Indiana’s ash pond closure plan. See Note 4 for more information on Hoosier Environmental Council's petition. The incremental amount recorded represents the discounted cash flows for estimated closure costs based upon the probability weightings of the potential closure methods as evaluated on a site-by-site basis.

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