Organization and Basis of Presentation (Policy)	6 Months Ended
Organization and Basis of Presentation (Policy)	Jun. 30, 2017
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Basis of Accounting	The results of operations of the International Disposal Group have been classified as Discontinued Operations on the Condensed Consolidated Statements of 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 Condensed Consolidated Financial Statements exclude amounts related to discontinued operations. Piedmont's results of operations and cash flows are included in the accompanying condensed consolidated financial statements of Duke Energy for the three and six months ended June 30, 2017, but not for the three and six months ended June 30, 2016, as Piedmont's earnings and cash flows are only included in Duke Energy's consolidated results subsequent to the acquisition date. BASIS OF PRESENTATION These Condensed Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles (GAAP) in the U.S. for interim financial information and with the instructions to Form 10-Q and Regulation S-X. Accordingly, these Condensed Consolidated Financial Statements do not include all information and notes required by GAAP in the U.S. for annual financial statements. Since the interim Condensed Consolidated Financial Statements and Notes do not include all information and notes required by GAAP in the U.S. for annual financial statements, the Condensed Consolidated Financial Statements and other information included in this quarterly report should be read in conjunction with the Consolidated Financial Statements and Notes in the Duke Energy Registrants’ combined Annual Report on Form 10-K for the year ended December 31, 2016, and the Consolidated Financial Statements and Notes in the Piedmont Annual Report on Form 10‑K for the year ended October 31, 2016. Effective November 1, 2016, Piedmont's fiscal year-end was changed from October 31 to December 31, the year-end of Duke Energy. A transition report was filed on Form 10-Q (Form 10-QT) as of December 31, 2016, for the transition period from November 1, 2016 to December 31, 2016. The information in these combined notes relates to each of the Duke Energy Registrants as noted in the Index to Combined Notes to Condensed Consolidated Financial Statements. However, none of the registrants make any representations as to information related solely to Duke Energy or the subsidiaries of Duke Energy other than itself. These Condensed Consolidated Financial Statements, in the opinion of the respective companies’ management, reflect all normal recurring adjustments necessary to fairly present the financial position and results of operations of each of the Duke Energy Registrants. Amounts reported in Duke Energy’s interim Condensed Consolidated Statements of Operations and each of the Subsidiary Registrants’ interim Condensed Consolidated Statements of Operations and Comprehensive Income are not necessarily indicative of amounts expected for the respective annual periods due to effects of seasonal temperature variations on energy consumption, regulatory rulings, timing of maintenance on electric generating units, changes in mark-to-market valuations, changing commodity prices and other factors.
Consolidation	These Condensed Consolidated Financial Statements include, after eliminating intercompany transactions and balances, the accounts of the Duke Energy Registrants and subsidiaries where the respective Duke Energy Registrants have control. These Condensed Consolidated Financial Statements also reflect the Duke Energy Registrants’ proportionate share of certain jointly owned generation and transmission facilities.
Use of Estimates	In preparing financial statements that conform to GAAP, management 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.
Unbilled Revenue	UNBILLED REVENUE Revenues on sales of electricity and natural gas are recognized when service is provided or the product is delivered. Unbilled revenues are recognized by applying customer billing rates to the estimated volumes of energy and natural gas delivered but not yet billed. Unbilled revenues can vary significantly from period to period as a result of seasonality, weather, customer usage patterns, customer mix, average price in effect for customer classes, timing of rendering customer bills, meter reading schedules, and the impact of weather normalization or margin decoupling mechanisms.
Inventory	INVENTORY Inventory is used for operations and is recorded primarily using the average cost method. Inventory related to regulated operations is valued at historical cost. Inventory related to nonregulated operations is valued at the lower of cost or market. Materials and supplies are recorded as inventory when purchased and subsequently charged to expense or capitalized to property, plant and equipment when installed. Inventory, including excess or obsolete inventory, is written-down to the lower of cost or market value. Once inventory has been written-down, it creates a new cost basis for the inventory that is not subsequently written-up.
Excise Taxes	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. Otherwise, excise taxes are accounted for on a net basis.
New Accounting Standards	NEW ACCOUNTING STANDARDS The new accounting standards adopted for 2017 and 2016 had no material impact on the presentation or results of operations, cash flows or financial position of the Duke Energy Registrants. While immaterial, adoption of the following accounting standard had the most significant impact on the Duke Energy results of operations, cash flows and financial position for the six months ended June 30, 2017. Stock-Based Compensation and Income Taxes. In first quarter 2017, Duke Energy adopted Financial Accounting Standards Board (FASB) guidance, which revised the accounting for stock-based compensation and the associated income taxes. The adopted guidance changes certain aspects of accounting for stock-based payment awards to employees including the accounting for income taxes and classification on the Condensed Consolidated Statements of Cash Flows. The primary impact to Duke Energy as a result of implementing this guidance was a cumulative-effect adjustment to retained earnings for tax benefits not previously recognized and additional income tax expense for the six months ended June 30, 2017. See the Duke Energy Condensed Consolidated Statements of Changes in Equity for further information. The following new Accounting Standards Updates (ASUs) have been issued, but have not yet been adopted by Duke Energy, as of June 30, 2017. Retirement Benefits. In March 2017, the FASB issued revised accounting guidance for the presentation of net periodic costs related to benefit plans. Current GAAP permits the aggregation of all the components of net periodic costs on the income statement and does not require the disclosure of the location of net periodic costs on the Condensed Consolidated Statement of Operations. Under the amended guidance, the service cost component of net periodic costs must be included within Operating income within the same line as other compensation expenses. All other components of net periodic costs must be outside of Operating income. In addition, the updated guidance permits only the service cost component of net periodic costs to be capitalized to Inventory or Property, Plant and Equipment. This represents a change from current GAAP, which permits all components of net periodic costs to be capitalized. The guidance allows for a practical expedient that permits a company to use amounts disclosed in prior-period financial statements as the estimation basis for applying the retrospective presentation requirements. For Duke Energy, this guidance is effective for interim and annual periods beginning January 1, 2018. These amendments should be applied retrospectively for the presentation of the various components of net periodic costs and prospectively for the change in eligible costs to be capitalized. Duke Energy currently presents all of the components of net periodic costs that are not capitalized within Operation, maintenance and other on the Condensed Consolidated Statement of Operations. Under this updated guidance, Duke Energy will retrospectively reclassify all the components of net periodic costs except for the service cost component to be presented outside of Operating income. However, Duke Energy will continue to present the service cost amount not capitalized within Operation, maintenance and other as this line item includes other compensation expense. Duke Energy is currently evaluating the financial statement impact, if any, of adopting this standard and whether or not the practical expedient will be utilized. Goodwill Impairment. In January 2017, the FASB issued revised guidance for subsequent measurement of goodwill. Under the guidance, a company will recognize an impairment to goodwill for the amount by which a reporting unit's carrying value exceeds the reporting unit's fair value, not to exceed the amount of goodwill allocated to that reporting unit. For Duke Energy, this guidance is effective for interim and annual periods beginning January 1, 2020. However, Duke Energy expects to early adopt this guidance on a prospective basis for the next annual goodwill impairment test. Duke Energy does not expect adopting this guidance will have a material impact to its results of operations or financial position. Revenue from Contracts with Customers. In May 2014, the FASB issued revised accounting guidance for revenue recognition from contracts with customers. The core principle of this guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The amendments in this update also require disclosure of sufficient information to allow users to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Most of Duke Energy’s revenue is expected to be in scope of the new guidance. The majority of our sales, including energy provided to residential customers, are from tariff offerings that provide natural gas or electricity without a defined contractual term ("at-will"). For such arrangements, Duke Energy expects that the revenue from contracts with customers will be equivalent to the electricity or natural gas supplied and billed in that period (including estimated billings). As such, Duke Energy does not expect that there will be a significant shift in the timing or pattern of revenue recognition for such sales. The evaluation of other revenue streams is ongoing, including long-term contracts with industrial customers and long-term purchase power agreements (PPA). Duke Energy continues to evaluate what information would be most useful for users of the financial statements, including information already provided in disclosures outside of the financial statement footnotes. These additional disclosures could include the disaggregation of revenues by geographic location, type of service, customer class or by duration of contract ("at-will" versus contracted revenue). Revenues from contracts with customers, revenue recognized under regulated operations accounting and revenue from lease accounting will also be disclosed. Duke Energy intends to use the modified retrospective method of adoption effective January 1, 2018. This method results in a cumulative-effect adjustment that will be recorded to retained earnings as of January 1, 2018, as if the standard had always been in effect. Disclosures for 2018 will include a comparison to what would have been reported for 2018 under the current revenue recognition rules in order to assist financial statement users in understanding how revenue recognition has changed as a result of this standard and to facilitate comparability with prior year reported results, which are not restated under the modified retrospective approach. Leases. In February 2016, the FASB issued revised accounting guidance for leases. The core principle of this guidance is that a lessee should recognize the assets and liabilities that arise from leases on the balance sheet. For Duke Energy, this guidance is effective for interim and annual periods beginning January 1, 2019, although it can be early adopted. The guidance is applied using a modified retrospective approach. Duke Energy is currently evaluating the financial statement impact of adopting this standard and is continuing to monitor industry implementation issues, including easements, pole attachments and renewable power purchase agreements. Other than an expected increase in assets and liabilities, the ultimate impact of the new standard has not yet been determined. Significant system enhancements may be required to facilitate the identification, tracking and reporting of potential leases based upon requirements of the new lease standard. Statement of Cash Flows. In November 2016, the FASB issued revised accounting guidance to reduce diversity in practice for the presentation and classification of restricted cash on the statement of cash flows. Under the updated guidance, restricted cash and restricted cash equivalents will be included within beginning-of-period and end-of-period cash and cash equivalents on the statement of cash flows. For Duke Energy, this guidance is effective for the interim and annual periods beginning January 1, 2018, although it can be early adopted. The guidance will be applied using a retrospective transition method to each period presented. Upon adoption by Duke Energy, the revised guidance will result in a change to the amount of cash and cash equivalents and restricted cash explained when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. Prior to adoption, the Duke Energy Registrants reflect changes in restricted cash within Cash Flows from Investing Activities on the Condensed Consolidated Statement of Cash Flows. Financial Instruments Classification and Measurement. In January 2016, the FASB issued revised accounting guidance for the classification and measurement of financial instruments. Changes in the fair value of all equity securities will be required to be recorded in net income. Current GAAP allows some changes in fair value for available-for-sale equity securities to be recorded in Accumulated other comprehensive income (AOCI). Additional disclosures will be required to present separately the financial assets and financial liabilities by measurement category and form of financial asset. An entity's equity investments that are accounted for under the equity method of accounting are not included within the scope of the new guidance. For Duke Energy, the revised accounting guidance is effective for interim and annual periods beginning January 1, 2018, by recording a cumulative-effect adjustment to retained earnings as of January 1, 2018. This guidance is expected to have minimal impact on the Duke Energy Registrant's Condensed Consolidated Statements of Operations and Comprehensive Income as changes in the fair value of most of the Duke Energy Registrants' available-for-sale equity securities are deferred as regulatory assets or liabilities pursuant to accounting guidance for regulated operations.
Acquisitions	The fair value of Piedmont's assets and liabilities were determined based on significant estimates and assumptions that are judgmental in nature, including the amount and timing of projected future cash flows, discount rates reflecting risk inherent in the future cash flows and market prices of long-term debt.
Environmental Costs	Liabilities are recorded when losses become probable and are reasonably estimable. Costs are typically expensed as Operation, maintenance and other on the Condensed Consolidated Statements of Operations unless regulatory recovery of the costs is deemed probable.
Derivatives	Duke Energy’s interest rate swaps for its regulated operations employ regulatory accounting. With regulatory accounting, the mark-to-market gains or losses on the swaps are deferred as regulatory liabilities or regulatory assets, respectively. Regulatory assets and liabilities are amortized consistent with the treatment of the related costs in the ratemaking process. The accrual of interest on the swaps is recorded as Interest Expense. For the Subsidiary Registrants, bulk power electricity and coal and natural gas purchases flow through fuel adjustment clauses, formula based contracts or other cost sharing mechanisms. Differences between the costs included in rates and the incurred costs, including undesignated derivative contracts, are largely deferred as regulatory assets or regulatory liabilities.
Investments	Unrealized gains and losses on all other AFS securities are included in other comprehensive income until realized, unless it is determined the carrying value of an investment is other-than-temporarily impaired. The Duke Energy Registrants analyze all investment holdings each reporting period to determine whether a decline in fair value should be considered other-than-temporary. If an OTTI exists, the unrealized credit loss is included in earnings. As a result, the ability to hold investments in unrealized loss positions is outside the control of the Duke Energy Registrants. Accordingly, all unrealized losses associated with debt and equity securities within the Investment Trusts are considered other-than-temporary impairments (OTTIs) and are recognized immediately. Investments within the Investment Trusts generally qualify for regulatory accounting, and accordingly realized and unrealized gains and losses are deferred as a regulatory asset or liability.
Earnings Per Share	Basic Earnings Per Share (EPS) is computed by dividing net income attributable to Duke Energy common stockholders, as adjusted for distributed and undistributed earnings allocated to participating securities, by the weighted average number of common shares outstanding during the period. Diluted EPS is computed by dividing net income attributable to Duke Energy common stockholders, as adjusted for distributed and undistributed earnings allocated to participating securities, by the diluted weighted average number of common shares outstanding during the period. Diluted EPS reflects the potential dilution that could occur if securities or other agreements to issue common stock, such as stock options and equity forward sale agreements, were exercised or settled.
Stock-based Compensation	For employee awards, equity classified stock-based compensation cost is measured at the service inception date or the grant date, based on the estimated achievement of certain performance metrics or the fair value of the award, and is recognized as expense or capitalized as a component of property, plant and equipment over the requisite service period.
Duke Energy Ohio [Member]
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Unbilled Revenue	Additionally, Duke Energy Ohio and Duke Energy Indiana sell nearly all of their retail accounts receivable to an affiliate, Cinergy Receivables Company, LLC (CRC), on a revolving basis. These transfers of receivables are accounted for as sales and include receivables for unbilled revenues. Accordingly, the receivables sold are not reflected on the Condensed Consolidated Balance Sheets of Duke Energy Ohio and Duke Energy Indiana.
Duke Energy Indiana [Member]
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Unbilled Revenue	Additionally, Duke Energy Ohio and Duke Energy Indiana sell nearly all of their retail accounts receivable to an affiliate, Cinergy Receivables Company, LLC (CRC), on a revolving basis. These transfers of receivables are accounted for as sales and include receivables for unbilled revenues. Accordingly, the receivables sold are not reflected on the Condensed Consolidated Balance Sheets of Duke Energy Ohio and Duke Energy Indiana.