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Summary of Significant Accounting Policies | 12 Months Ended
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Dec. 31, 2023
Accounting Policies [Abstract] |
Summary of Significant Accounting Policies | SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations and Basis of Consolidation Duke Energy is an energy company headquartered in Charlotte, North Carolina, subject to regulation by the FERC and other regulatory agencies listed below. Duke Energy operates in the U.S. primarily through its direct and indirect subsidiaries. Certain Duke Energy subsidiaries are also subsidiary registrants, including Duke Energy Carolinas; Progress Energy; Duke Energy Progress; Duke Energy Florida; Duke Energy Ohio; Duke Energy Indiana and Piedmont. When discussing Duke Energy’s consolidated financial information, it necessarily includes the results of its separate Subsidiary Registrants, which along with Duke Energy, are collectively referred to as the Duke Energy Registrants. The information in these combined notes relates to each of the Duke Energy Registrants as noted in the Index to Combined Notes to Consolidated Financial Statements. However, none of the Subsidiary Registrants make any representation as to information related solely to Duke Energy or the Subsidiary Registrants of Duke Energy other than itself. These Consolidated Financial Statements include, after eliminating intercompany transactions and balances, the accounts of the Duke Energy Registrants and subsidiaries or VIEs where the respective Duke Energy Registrants have control. See Note 18 for additional information on VIEs. These Consolidated Financial Statements also reflect the Duke Energy Registrants’ proportionate share of certain jointly owned generation and transmission facilities. See Note 9 for additional information on joint ownership. Substantially all of the Subsidiary Registrants' operations qualify for regulatory accounting. Duke Energy Carolinas is a regulated public utility primarily engaged in the generation, transmission, distribution and sale of electricity in portions of North Carolina and South Carolina. Duke Energy Carolinas is subject to the regulatory provisions of the NCUC, PSCSC, NRC and FERC. Progress Energy is a public utility holding company, which conducts operations through its wholly owned subsidiaries, Duke Energy Progress and Duke Energy Florida. Progress Energy is subject to regulation by FERC and other regulatory agencies listed below. Duke Energy Progress is a regulated public utility primarily engaged in the generation, transmission, distribution and sale of electricity in portions of North Carolina and South Carolina. Duke Energy Progress is subject to the regulatory provisions of the NCUC, PSCSC, NRC and FERC. Duke Energy Florida is a regulated public utility primarily engaged in the generation, transmission, distribution and sale of electricity in portions of Florida. Duke Energy Florida is subject to the regulatory provisions of the FPSC, NRC and FERC. Duke Energy Ohio is a regulated public utility primarily engaged in the transmission and distribution of electricity in portions of Ohio and Kentucky, the generation and sale of electricity in portions of Kentucky and the transportation and sale of natural gas in portions of Ohio and Kentucky. Duke Energy Ohio conducts competitive auctions for retail electricity supply in Ohio whereby the energy price is recovered from retail customers and recorded in Operating Revenues on the Consolidated Statements of Operations and Comprehensive Income. Operations in Kentucky are conducted through its wholly owned subsidiary, Duke Energy Kentucky. References herein to Duke Energy Ohio collectively include Duke Energy Ohio and its subsidiaries, unless otherwise noted. Duke Energy Ohio is subject to the regulatory provisions of the PUCO, KPSC and FERC. Duke Energy Indiana is a regulated public utility primarily engaged in the generation, transmission, distribution and sale of electricity in portions of Indiana. Duke Energy Indiana is subject to the regulatory provisions of the IURC and FERC. Piedmont is a regulated public utility primarily engaged in the distribution of natural gas in portions of North Carolina, South Carolina and Tennessee. Piedmont is subject to the regulatory provisions of the NCUC, PSCSC, TPUC and FERC. Certain prior year amounts have been reclassified to conform to the current year presentation. Other Current Assets and Liabilities The following table provides a description of amounts included in Other within Current Assets or Current Liabilities that exceed 5% of total Current Assets or Current Liabilities on the Duke Energy Registrants' Consolidated Balance Sheets at either December 31, 2023, or 2022.
|  |  | December 31,
(in millions) | Location |  | 2023 |  | 2022
Duke Energy Carolinas |  |  |  |  |
Accrued compensation | Current Liabilities |  | $ | 224 |  |  | $ | 247 |
Duke Energy Florida |  |  |  |  |
Customer deposits/Collateral liabilities | Current Liabilities |  | $ | 168 |  |  | $ | 200 |
Duke Energy Ohio |  |  |  |  |
Gas Storage | Current Assets |  | $ | 23 |  |  | $ | 57 |
Tax receivables | Current Assets |  | 95 |  |  | 4 |
Duke Energy Indiana |  |  |  |  |
Mark-to-market transactions | Current Assets |  | $ | 18 |  |  | $ | 110 |
Customer advances | Current Liabilities |  | $ | 87 |  |  | $ | 51 |
Discontinued Operations Duke Energy has elected to present cash flows of discontinued operations combined with cash flows of continuing operations. Unless otherwise noted, the notes to these consolidated financial statements exclude amounts related to discontinued operations for all periods presented. For the years ended December 31, 2023, 2022 and 2021, the Loss From Discontinued Operations, net of tax on Duke Energy's Consolidated Statements of Operations includes amounts related to noncontrolling interests. A portion of Noncontrolling interests on Duke Energy's Consolidated Balance Sheets relates to discontinued operations for the periods presented. See Note 2 for discussion of discontinued operations related to the Commercial Renewables Disposal Groups. Noncontrolling Interest Duke Energy maintains a controlling financial interest in certain less than wholly owned subsidiaries. As a result, Duke Energy consolidates these subsidiaries and presents the third-party investors' portion of Duke Energy's net income (loss), net assets and comprehensive income (loss) as noncontrolling interest. Noncontrolling interest is included as a component of equity on the Consolidated Balance Sheets. Operating agreements of Duke Energy's subsidiaries with noncontrolling interest allocate profit and loss based on their pro rata shares of the ownership interest in the respective subsidiary. Therefore, Duke Energy allocates net income or loss and other comprehensive income or loss of these subsidiaries to the owners based on their pro rata shares. Significant Accounting Policies Use of Estimates In preparing financial statements that conform to GAAP, the Duke Energy Registrants must make estimates and assumptions that affect the reported amounts of assets and liabilities, the reported amounts of revenues and expenses and the disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. Regulatory Accounting The majority of the Duke Energy Registrants’ operations are subject to price regulation for the sale of electricity and natural gas by state utility commissions or FERC. When prices are set on the basis of specific costs of the regulated operations and an effective franchise is in place such that sufficient natural gas or electric services can be sold to recover those costs, the Duke Energy Registrants apply regulatory accounting. Regulatory accounting changes the timing of the recognition of costs or revenues relative to a company that does not apply regulatory accounting. As a result, regulatory assets and regulatory liabilities are recognized on the Consolidated Balance Sheets. Regulatory assets and liabilities are amortized consistent with the treatment of the related cost in the ratemaking process. Regulatory assets are reviewed for recoverability each reporting period. If a regulatory asset is no longer deemed probable of recovery, the deferred cost is charged to earnings. See Note 4 for further information. Regulatory accounting rules also require recognition of a disallowance (also called "impairment") loss if it becomes probable that part of the cost of a plant under construction (or a recently completed plant or an abandoned plant) will be disallowed for ratemaking purposes and a reasonable estimate of the amount of the disallowance can be made. For example, if a cost cap is set for a plant still under construction, the amount of the disallowance is a result of a judgment as to the ultimate cost of the plant. These disallowances can require judgments on allowed future rate recovery. When it becomes probable that regulated generation, transmission or distribution assets will be abandoned, the cost of the asset is removed from plant in service. The value that may be retained as a regulatory asset on the balance sheet for the abandoned property is dependent upon amounts that may be recovered through regulated rates, including any return. As such, an impairment charge could be partially or fully offset by the establishment of a regulatory asset if rate recovery is probable. The impairment charge for a disallowance of costs for regulated plants under construction, recently completed or abandoned is based on discounted cash flows. The Duke Energy Registrants utilize cost-tracking mechanisms, commonly referred to as fuel adjustment clauses or PGA clauses. These clauses allow for the recovery of fuel and fuel-related costs, portions of purchased power, natural gas costs and hedging costs through surcharges on customer rates. The difference between the costs incurred and the surcharge revenues is recorded either as an adjustment to Operating Revenues, Operating Expenses – Fuel used in electric generation or Operating Expenses – Cost of natural gas on the Consolidated Statements of Operations, with an off-setting impact on regulatory assets or liabilities. Cash, Cash Equivalents and Restricted Cash All highly liquid investments with maturities of three months or less at the date of acquisition are considered cash equivalents. Duke Energy, Progress Energy and Duke Energy Florida have restricted cash balances related primarily to collateral assets, escrow deposits and VIEs. Duke Energy Carolinas and Duke Energy Progress have restricted cash balances related to VIEs from storm recovery bonds issued. See Note 18 for additional information. Restricted cash amounts are included in Other within Current Assets and Other Noncurrent Assets on the Consolidated Balance Sheets. The following table presents the components of cash, cash equivalents and restricted cash included in the Consolidated Balance Sheets.
| December 31, 2023
|  |  | Duke |  |  |  | Duke |  | Duke
| Duke |  | Energy |  | Progress |  | Energy |  | Energy
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida
Current Assets |  |  |  |  |  |  |  |  |
Cash and cash equivalents | $ | 253 |  |  | $ | 9 |  |  | $ | 59 |  |  | $ | 18 |  |  | $ | 24 |
Other | 76 |  |  | 9 |  |  | 67 |  |  | 31 |  |  | 36 |
Other Noncurrent Assets |  |  |  |  |  |  |  |  |
Other | 16 |  |  | 1 |  |  | 9 |  |  | 2 |  |  | 7 |
Total cash, cash equivalents and restricted cash | $ | 345 |  |  | $ | 19 |  |  | $ | 135 |  |  | $ | 51 |  |  | $ | 67 |
| December 31, 2022
|  |  | Duke |  |  |  | Duke |  | Duke
| Duke |  | Energy |  | Progress |  | Energy |  | Energy
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida
Current Assets |  |  |  |  |  |  |  |  |
Cash and cash equivalents | $ | 409 |  |  | $ | 44 |  |  | $ | 108 |  |  | $ | 49 |  |  | $ | 45 |
Other | 82 |  |  | 8 |  |  | 74 |  |  | 28 |  |  | 41 |
Other Noncurrent Assets |  |  |  |  |  |  |  |  |
Other | 11 |  |  | 1 |  |  | 2 |  |  | 2 |  |  | — |
Total cash, cash equivalents and restricted cash | $ | 502 |  |  | $ | 53 |  |  | $ | 184 |  |  | $ | 79 |  |  | $ | 86 |
Inventory Inventory related to regulated operations is valued at historical cost. Inventory is charged to expense or capitalized to property, plant and equipment when issued, primarily using the average cost method. Excess or obsolete inventory is written down to the lower of cost or net realizable value. Once inventory has been written down, it creates a new cost basis for the inventory that is not subsequently written up. Provisions for inventory write-offs were not material at December 31, 2023, and 2022, respectively. The components of inventory are presented in the tables below.
| December 31, 2023
|  |  | Duke |  |  |  | Duke |  | Duke |  | Duke |  | Duke |  |
| Duke |  | Energy |  | Progress |  | Energy |  | Energy |  | Energy |  | Energy |  |
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida |  | Ohio |  | Indiana |  | Piedmont
Materials and supplies | $ | 3,086 |  |  | $ | 1,075 |  |  | $ | 1,465 |  |  | $ | 963 |  |  | $ | 502 |  |  | $ | 139 |  |  | $ | 361 |  |  | $ | 12 |
Coal | 842 |  |  | 364 |  |  | 231 |  |  | 154 |  |  | 77 |  |  | 28 |  |  | 219 |  |  | — |
Natural gas, oil and other | 364 |  |  | 45 |  |  | 205 |  |  | 110 |  |  | 95 |  |  | 12 |  |  | 2 |  |  | 100 |
Total inventory | $ | 4,292 |  |  | $ | 1,484 |  |  | $ | 1,901 |  |  | $ | 1,227 |  |  | $ | 674 |  |  | $ | 179 |  |  | $ | 582 |  |  | $ | 112 |
| December 31, 2022
|  |  | Duke |  |  |  | Duke |  | Duke |  | Duke |  | Duke |  |
| Duke |  | Energy |  | Progress |  | Energy |  | Energy |  | Energy |  | Energy |  |
(in millions) | Energy |  | Carolinas |  | Energy |  | Progress |  | Florida |  | Ohio |  | Indiana |  | Piedmont
Materials and supplies | $ | 2,604 |  |  | $ | 876 |  |  | $ | 1,232 |  |  | $ | 819 |  |  | $ | 413 |  |  | $ | 105 |  |  | $ | 342 |  |  | $ | 12 |
Coal | 620 |  |  | 253 |  |  | 190 |  |  | 99 |  |  | 91 |  |  | 34 |  |  | 144 |  |  | — |
Natural gas, oil and other | 360 |  |  | 35 |  |  | 157 |  |  | 88 |  |  | 69 |  |  | 5 |  |  | 3 |  |  | 160 |
Total inventory | $ | 3,584 |  |  | $ | 1,164 |  |  | $ | 1,579 |  |  | $ | 1,006 |  |  | $ | 573 |  |  | $ | 144 |  |  | $ | 489 |  |  | $ | 172 |
Investments in Debt and Equity Securities The Duke Energy Registrants classify investments in equity securities as FV-NI and investments in debt securities as AFS. Both categories are recorded at fair value on the Consolidated Balance Sheets. Realized and unrealized gains and losses on securities classified as FV-NI are reported through net income. Unrealized gains and losses for debt securities classified as AFS are included in AOCI until realized, unless it is determined the carrying value of an investment has a credit loss. For certain investments of regulated operations, such as substantially all of the NDTF, realized and unrealized gains and losses (including any credit losses) on debt securities are recorded as a regulatory asset or liability. The credit loss portion of debt securities of nonregulated operations are included in earnings. Investments in debt and equity securities are classified as either current or noncurrent based on management’s intent and ability to sell these securities, taking into consideration current market liquidity. See Note 16 for further information. Goodwill Duke Energy, Progress Energy, Duke Energy Ohio and Piedmont perform annual goodwill impairment tests as of August 31 each year at the reporting unit level, which is determined to be a business segment or one level below. Duke Energy, Progress Energy, Duke Energy Ohio and Piedmont update these tests between annual tests if events or circumstances occur that would more likely than not reduce the fair value of a reporting unit below its carrying value. See Note 12 for further information. Intangible Assets Intangible assets are included in Other in Other Noncurrent Assets on the Consolidated Balance Sheets. Generally, intangible assets are amortized using an amortization method that reflects the pattern in which the economic benefits of the intangible asset are consumed or on a straight-line basis if that pattern is not readily determinable. Amortization of intangibles is reflected in Depreciation and amortization on the Consolidated Statements of Operations. Intangible assets are subject to impairment testing and if impaired, the carrying value is accordingly reduced. RECs are used to measure compliance with renewable energy standards and are held primarily for consumption. See Note 12 for further information. Long-Lived Asset Impairments The Duke Energy Registrants evaluate long-lived assets that are held and used, excluding goodwill, for impairment when circumstances indicate the carrying value of those assets may not be recoverable. An impairment exists when a long-lived asset’s carrying value exceeds the estimated undiscounted cash flows expected to result from the use and eventual disposition of the asset. The estimated cash flows may be based on alternative expected outcomes that are probability weighted. If the carrying value of the long-lived asset is not recoverable based on these estimated future undiscounted cash flows, the carrying value of the asset is written down to its then current estimated fair value and an impairment charge is recognized. The Duke Energy Registrants assess fair value of long-lived assets that are held and used using various methods, including recent comparable third-party sales, internally developed discounted cash flow analysis and analysis from outside advisors. Triggering events to reassess cash flows may include, but are not limited to, significant changes in commodity prices, the condition of an asset or management’s interest in selling the asset. Property, Plant and Equipment Property, plant and equipment are stated at the lower of depreciated historical cost net of any disallowances or fair value, if impaired. The Duke Energy Registrants capitalize all construction-related direct labor and material costs, as well as indirect construction costs such as general engineering, taxes and financing costs. See “Allowance for Funds Used During Construction and Interest Capitalized” section below for information on capitalized financing costs. Costs of renewals and betterments that extend the useful life of property, plant and equipment are also capitalized. The cost of repairs, replacements and major maintenance projects, which do not extend the useful life or increase the expected output of the asset, are expensed as incurred. Depreciation is generally computed over the estimated useful life of the asset using the composite straight-line method. Depreciation studies are conducted periodically to update composite rates and are approved by state utility commissions and/or the FERC when required. The composite weighted average depreciation rates, excluding nuclear fuel, are included in the table that follows.
| Years Ended December 31,
| 2023 |  | 2022 |  | 2021
Duke Energy | 2.9 | % |  | 3.0 | % |  | 2.9 | %
Duke Energy Carolinas | 2.7 | % |  | 2.7 | % |  | 2.7 | %
Progress Energy | 3.3 | % |  | 3.2 | % |  | 3.1 | %
Duke Energy Progress | 3.1 | % |  | 3.0 | % |  | 3.0 | %
Duke Energy Florida | 3.5 | % |  | 3.5 | % |  | 3.3 | %
Duke Energy Ohio | 2.8 | % |  | 2.9 | % |  | 2.9 | %
Duke Energy Indiana | 3.6 | % |  | 3.6 | % |  | 3.6 | %
Piedmont | 2.1 | % |  | 2.1 | % |  | 2.1 | %
In general, when the Duke Energy Registrants retire regulated property, plant and equipment, the original cost plus the cost of retirement, less salvage value and any depreciation already recognized, is charged to accumulated depreciation. However, when it becomes probable the asset will be retired substantially in advance of its original expected useful life or is abandoned, the cost of the asset and the corresponding accumulated depreciation is recognized as a separate asset. If the asset is still in operation, the net amount is classified as Facilities to be retired, net on the Consolidated Balance Sheets. If the asset is no longer operating, the net amount is classified in Regulatory assets on the Consolidated Balance Sheets if deemed recoverable (see discussion of long-lived asset impairments above). The carrying value of the asset is based on historical cost if the Duke Energy Registrants are allowed to recover the remaining net book value and a return equal to at least the incremental borrowing rate. If not, an impairment is recognized to the extent the net book value of the asset exceeds the present value of future revenues discounted at the incremental borrowing rate. When the Duke Energy Registrants sell entire regulated operating units, the original cost and accumulated depreciation and amortization balances are removed from Property, Plant and Equipment on the Consolidated Balance Sheets. Any gain or loss is recorded in earnings, unless otherwise required by the applicable regulatory body. See Note 11 for additional information. Other Noncurrent Assets Duke Energy, through a nonregulated subsidiary, was the winner of the Carolina Long Bay offshore wind auction in May 2022 and recorded an asset of $150 million related to the contract in Other within Other noncurrent assets on the Consolidated Balance Sheets as of December 31, 2023 and 2022. The asset is recorded at historical cost and is subject to impairment testing should circumstances indicate the carrying value may not be recoverable. In November 2022, Duke Energy committed to a plan to sell the Commercial Renewables business segment, excluding the offshore wind contract for Carolina Long Bay, which was moved to the EU&I segment. See Notes 2 and 3 for further information. Leases Duke Energy determines if an arrangement is a lease at contract inception based on whether the arrangement involves the use of a physically distinct identified asset and whether Duke Energy has the right to obtain substantially all of the economic benefits from the use of the asset throughout the period as well as the right to direct the use of the asset. As a policy election, Duke Energy does not evaluate arrangements with initial contract terms of less than one year as leases. Operating leases are included in Operating lease ROU assets, net, Other current liabilities and Operating lease liabilities on the Consolidated Balance Sheets. Finance leases are included in Property, Plant and Equipment, Current maturities of long-term debt and Long-Term Debt on the Consolidated Balance Sheets. For lessee and lessor arrangements, Duke Energy has elected a policy to not separate lease and non-lease components for all asset classes. For lessor arrangements, lease and non-lease components are only combined under one arrangement and accounted for under the lease accounting framework if the non-lease components are not the predominant component of the arrangement and the lease component would be classified as an operating lease. Nuclear Fuel Nuclear fuel is classified as Property, Plant and Equipment on the Consolidated Balance Sheets. Nuclear fuel in the front-end fuel processing phase is considered work in progress and not amortized until placed in service. Amortization of nuclear fuel is included within Fuel used in electric generation and purchased power on the Consolidated Statements of Operations. Amortization is recorded using the units-of-production method. Allowance for Funds Used During Construction and Interest Capitalized For regulated operations, the debt and equity costs of financing the construction of property, plant and equipment are reflected as AFUDC and capitalized as a component of the cost of property, plant and equipment. AFUDC equity is reported on the Consolidated Statements of Operations as non-cash income in Other income and expenses, net. AFUDC debt is reported as a non-cash offset to Interest Expense. After construction is completed, the Duke Energy Registrants are permitted to recover these costs through their inclusion in rate base and the corresponding subsequent depreciation or amortization of those regulated assets. AFUDC equity, a permanent difference for income taxes, reduces the ETR when capitalized and increases the ETR when depreciated or amortized. See Note 24 for additional information. Asset Retirement Obligations AROs are recognized for legal obligations associated with the retirement of property, plant and equipment. When recording an ARO, the present value of the projected liability is recognized in the period in which it is incurred, if a reasonable estimate of fair value can be made. The liability is accreted over time. For operating plants, the present value of the liability is added to the cost of the associated asset and depreciated over the remaining life of the asset. For retired plants, the present value of the liability is recorded as a regulatory asset unless determined not to be probable of recovery. The present value of the initial obligation and subsequent updates are based on discounted cash flows, which include estimates regarding timing of future cash flows, selection of discount rates and cost escalation rates, among other factors. These estimates are subject to change. Depreciation expense is adjusted prospectively for any changes to the carrying amount of the associated asset. The Duke Energy Registrants receive amounts to fund the cost of the ARO for regulated operations through a combination of regulated revenues and earnings on the NDTF. As a result, amounts recovered in regulated revenues, earnings on the NDTF, accretion expense and depreciation of the associated asset are netted and deferred as a regulatory asset or liability. Accounts Payable Duke Energy has a voluntary supply chain finance program (the “program”) that allows Duke Energy suppliers, at their sole discretion, to sell their receivables from Duke Energy to a global financial institution at a rate that leverages Duke Energy’s credit rating and, which may result in favorable terms compared to the rate available to the supplier on their own credit rating. Suppliers participating in the program, determine at their sole discretion which invoices they will sell to the financial institution. Suppliers’ decisions on which invoices are sold do not impact Duke Energy’s payment terms, which are based on commercial terms negotiated between Duke Energy and the supplier regardless of program participation. The commercial terms negotiated between Duke Energy and its suppliers are consistent regardless of whether the supplier elects to participate in the program. Duke Energy does not issue any guarantees with respect to the program and does not participate in negotiations between suppliers and the financial institution. Duke Energy does not have an economic interest in the supplier’s decision to participate in the program and receives no interest, fees or other benefit from the financial institution based on supplier participation in the program. The following table presents the outstanding accounts payable balance sold to the financial institution by our suppliers and the supplier invoices sold to the financial institution under the program included within Net cash provided by operating activities on the Consolidated Statements of Cash Flows as of December 31, 2023, and December 31, 2022.
| For the Years Ended December 31, 2022 and 2023 |  |
|  | Duke |  | Duke | Duke | Duke | Duke |  |  |  |  |  |  |
| Duke | Energy | Progress | Energy | Energy | Energy | Energy |  |  |  |  |  |  |
(in millions) | Energy | Carolinas | Energy | Progress | Florida | Ohio | Indiana | Piedmont |  |  |  |  |  |
Confirmed obligations outstanding at December 31, 2021 | $ | 19 |  | $ | — |  | $ | 9 |  | $ | — |  | $ | 9 |  | $ | 6 |  | $ | — |  | $ | 4 |  |  |  |  |  |  |
Invoices confirmed during the period | 283 |  | 29 |  | 76 |  | 26 |  | 50 |  | 32 |  | 2 |  | 145 |  |  |  |  |  |  |
Confirmed invoices paid during the period | (215) |  | (23) |  | (66) |  | (18) |  | (48) |  | (33) |  | (2) |  | (92) |  |  |  |  |  |  |
Confirmed obligations outstanding at December 31, 2022 | $ | 87 |  | $ | 6 |  | $ | 19 |  | $ | 8 |  | $ | 11 |  | $ | 5 |  | $ | — |  | $ | 57 |  |  |  |  |  |  |
Invoices confirmed during the period | 228 |  | 24 |  | 58 |  | 22 |  | 36 |  | 7 |  | — |  | 139 |  |  |  |  |  |  |
Confirmed invoices paid during the period | (265) |  | (30) |  | (74) |  | (30) |  | (44) |  | (12) |  | — |  | (149) |  |  |  |  |  |  |
Confirmed obligations outstanding at December 31, 2023 | $ | 50 |  | $ | — |  | $ | 3 |  | $ | — |  | $ | 3 |  | $ | — |  | $ | — |  | $ | 47 |  |  |  |  |  |  |
Revenue Recognition Duke Energy recognizes revenue as customers obtain control of promised goods and services in an amount that reflects consideration expected in exchange for those goods or services. Generally, the delivery of electricity and natural gas results in the transfer of control to customers at the time the commodity is delivered and the amount of revenue recognized is equal to the amount billed to each customer, including estimated volumes delivered when billings have not yet occurred. See Note 19 for further information. Alternative Revenue Programs Duke Energy accounts for certain types of programs established by the regulators in the states in which it operates, including decoupling mechanisms, as alternative revenue programs. Alternative revenue programs are contracts between an entity and its regulator, not a contract between an entity and a customer. Revenue arising from alternative revenue programs is presented as Regulated electric revenues and Regulated natural gas revenues on the Consolidated Statements of Operations. Revenue from alternative revenue programs is recognized in the period they are earned (i.e. during the period of revenue shortfall or excess due to fluctuations in customer usage or when specific targets are met resulting in the achievement of performance incentives or penalties) and a regulatory asset or liability on the Consolidated Balance Sheets is established which is subsequently billed or refunded to customers. Duke Energy recognizes revenue as alternative revenue programs for programs that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected within 24 months. See Note 19 for disaggregated revenue information including revenue from contracts with customers and revenues recognized as alternative revenue programs. Derivatives and Hedging Derivative and non-derivative instruments may be used in connection with commodity price and interest rate activities, including swaps, futures, forwards and options. All derivative instruments, except those that qualify for the NPNS exception, are recorded on the Consolidated Balance Sheets at fair value. Qualifying derivative instruments may be designated as either cash flow hedges or fair value hedges. Other derivative instruments (undesignated contracts) either have not been designated or do not qualify as hedges. The effective portion of the change in the fair value of cash flow hedges is recorded in AOCI. The effective portion of the change in the fair value of a fair value hedge is offset in net income by changes in the hedged item. For activity subject to regulatory accounting, gains and losses on derivative contracts are reflected as regulatory assets or liabilities and not as other comprehensive income or current period income. As a result, changes in fair value of these derivatives have no immediate earnings impact. Formal documentation, including transaction type and risk management strategy, is maintained for all contracts accounted for as a hedge. At inception and at least every three months thereafter, the hedge contract is assessed to see if it is highly effective in offsetting changes in cash flows or fair values of hedged items. See Note 15 for further information. Captive Insurance Reserves Duke Energy has captive insurance subsidiaries that provide coverage, on an indemnity basis, to the Subsidiary Registrants as well as certain third parties, on a limited basis, for financial losses, primarily related to property, workers’ compensation and general liability. Liabilities include provisions for estimated losses incurred but not reported (IBNR), as well as estimated provisions for known claims. IBNR reserve estimates are primarily based upon historical loss experience, industry data and other actuarial assumptions. Reserve estimates are adjusted in future periods as actual losses differ from experience. Duke Energy, through its captive insurance entities, also has reinsurance coverage with third parties for certain losses above a per occurrence and/or aggregate retention. Receivables for reinsurance coverage are recognized when realization is deemed probable. Preferred Stock Preferred stock is reviewed to determine the appropriate balance sheet classification and embedded features, such as call options, are evaluated to determine if they should be bifurcated and accounted for separately. Costs directly related to the issuance of preferred stock are recorded as a reduction of the proceeds received. The liability for the dividend is recognized when declared. The accumulated dividends on the cumulative preferred stock is recognized to net income available to Duke Energy Corporation in the EPS calculation. See Note 20 for further information. Loss Contingencies and Environmental Liabilities Contingent losses are recorded when it is probable a loss has occurred and the loss can be reasonably estimated. When a range of the probable loss exists and no amount within the range is a better estimate than any other amount, the minimum amount in the range is recorded. Unless otherwise required by GAAP, legal fees are expensed as incurred. Environmental liabilities are recorded on an undiscounted basis when environmental remediation or other liabilities become probable and can be reasonably estimated. Environmental expenditures related to past operations that do not generate current or future revenues are expensed. Environmental expenditures related to operations that generate current or future revenues are expensed or capitalized, as appropriate. Certain environmental expenditures receive regulatory accounting treatment and are recorded as regulatory assets. See Notes 4 and 5 for further information. Severance and Special Termination Benefits Duke Energy maintains severance plans for the general employee population under which, in general, the longer a terminated employee worked prior to termination the greater the amount of severance benefits provided. A liability for involuntary severance is recorded once an involuntary severance plan is committed to by management if involuntary severances are probable and can be reasonably estimated. For involuntary severance benefits incremental to its ongoing severance plan benefits, the fair value of the obligation is expensed at the communication date if there are no future service requirements or over the required future service period. Duke Energy also offers special termination benefits under voluntary severance programs. Special termination benefits are recorded immediately upon employee acceptance absent a significant retention period. Otherwise, the cost is recorded over the remaining service period. Employee acceptance of voluntary severance benefits is determined by management based on the facts and circumstances of the benefits being offered. See Note 21 for further information. Guarantees If necessary, liabilities are recognized at the time of issuance or material modification of a guarantee for the estimated fair value of the obligation it assumes. Fair value is estimated using a probability weighted approach. The obligation is reduced over the term of the guarantee or related contract in a systematic and rational method as risk is reduced. Duke Energy recognizes a liability for the best estimate of its loss due to the nonperformance of the guaranteed party. This liability is recognized at the inception of a guarantee and is updated periodically. See Note 8 for further information. Income Taxes Duke Energy and its subsidiaries file a consolidated federal income tax return and other state and foreign jurisdictional returns. The Subsidiary Registrants are parties to a tax-sharing agreement with Duke Energy. Income taxes recorded represent amounts the Subsidiary Registrants would incur as separate C-Corporations. Deferred income taxes have been provided for temporary differences between GAAP and tax bases of assets and liabilities because the differences create taxable or tax-deductible amounts for future periods. ITCs associated with regulated operations are deferred and amortized as a reduction of income tax expense over the estimated useful lives of the related properties. Accumulated deferred income taxes are valued using the enacted tax rate expected to apply to taxable income in the periods in which the deferred tax asset or liability is expected to be settled or realized. In the event of a change in tax rates, deferred tax assets and liabilities are remeasured as of the enactment date of the new rate. To the extent that the change in the value of the deferred tax represents an obligation to customers, the impact of the remeasurement is deferred to a regulatory liability. Remaining impacts are recorded in income from continuing operations. Duke Energy's results of operations could be impacted if the estimate of the tax effect of reversing temporary differences is not reflective of actual outcomes, is modified to reflect new developments or interpretations of the tax law, revised to incorporate new accounting principles, or changes in the expected timing or manner of a reversal. Tax-related interest and penalties are recorded in Interest Expense and Other income and expenses, net in the Consolidated Statements of Operations. See Note 24 for further information. Excise Taxes Certain excise taxes levied by state or local governments are required to be paid even if not collected from the customer. These taxes are recognized on a gross basis. Taxes for which Duke Energy operates merely as a collection agent for the state and local government are accounted for on a net basis. Excise taxes accounted for on a gross basis within both Operating Revenues and Property and other taxes in the Consolidated Statements of Operations were as follows.
| Years Ended December 31,
(in millions) | 2023 |  | 2022 |  | 2021
Duke Energy | $ | 458 |  |  | $ | 449 |  |  | $ | 420 |
Duke Energy Carolinas | 27 |  |  | 47 |  |  | 44 |
Progress Energy | 322 |  |  | 290 |  |  | 250 |
Duke Energy Progress | 5 |  |  | 25 |  |  | 22 |
Duke Energy Florida | 317 |  |  | 265 |  |  | 228 |
Duke Energy Ohio | 106 |  |  | 104 |  |  | 102 |
Duke Energy Indiana | 1 |  |  | 7 |  |  | 23 |
Piedmont | 2 |  |  | 1 |  |  | 1 |
Dividend Restrictions and Unappropriated Retained Earnings Duke Energy does not have any current legal, regulatory or other restrictions on paying common stock dividends to shareholders. However, if Duke Energy were to defer dividend payments on the preferred stock, the declaration of common stock dividends would be prohibited. See Note 20 for more information. Additionally, as further described in Note 4, Duke Energy Carolinas, Duke Energy Progress, Duke Energy Ohio, Duke Energy Indiana and Piedmont have restrictions on paying dividends or otherwise advancing funds to Duke Energy due to conditions established by regulators in conjunction with merger transaction approvals. At December 31, 2023, and 2022, an insignificant amount of Duke Energy’s consolidated Retained earnings balance represents undistributed earnings of equity method investments. New Accounting Standards The following accounting standard was adopted by the Duke Energy Registrants in 2021. Leases with Variable Lease Payments. In July 2021, the Financial Accounting Standards Board issued new accounting guidance requiring lessors to classify a lease with variable lease payments that do not depend on a reference index or rate as an operating lease if both of the following are met: (1) the lease would have to be classified as a sales-type or direct financing lease under prior guidance, and (2) the lessor would have recognized a day-one loss. Duke Energy elected to adopt the guidance immediately upon issuance of the new standard and will be applying the new standard prospectively to new lease arrangements meeting the criteria. Duke Energy did not have any lease arrangements that this new accounting guidance materially impacted.

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