Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X and, therefore, do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation in accordance with GAAP are reflected in the condensed consolidated financial statements. All adjustments are of a normal recurring nature, except as otherwise disclosed. The Balance Sheets at December 31, 2015 are derived from Talen Energy's 2015 audited Balance Sheet. The financial statements and notes thereto should be read in conjunction with the financial statements and notes contained in Talen Energy's 2015 Form 10-K. The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results to be expected for the full year ending December 31, 2016 or other future periods, because results for interim periods can be disproportionately influenced by various factors, developments and seasonal variations. Talen Energy Supply is considered the accounting predecessor of Talen Energy Corporation. Therefore, the financial information prior to the June 2015 spinoff presented in this Quarterly Report on Form 10-Q for both registrants includes only legacy Talen Energy Supply information. Talen Energy completed the acquisition of RJS Power in June 2015 and the acquisition of MACH Gen in November 2015. See Note 6 in Talen Energy's 2015 Form 10-K for additional information. RJS and MACH Gen's operating results for the three months ended March 31, 2016 are included in Talen Energy's results of operations with no comparable amounts for the same period in 2015. The assets and liabilities related to the Holtwood, Lake Wallenpaupack, C.P. Crane and Ironwood facilities were classified as "Assets held for sale" and "Liabilities held for sale" at December 31, 2015, while Holtwood and Lake Wallenpaupack remain classified as such at March 31, 2016. See Note 7 for additional information on these divestitures. The sales of Talen Ironwood Holdings, LLC and C.P. Crane LLC were completed in February 2016 and the sale of the Holtwood and Lake Wallenpaupack hydroelectric facilities was completed in April 2016. The sales satisfied the requirement to divest certain PJM assets to comply with a December 2014 FERC order approving the combination with RJS Power. The classification of certain prior period amounts has been changed to conform to the presentation in the March 31, 2016 financial statements as discussed below.
New Accounting Guidance	Effective January 1, 2016, Talen Energy adopted accounting guidance that simplifies the presentation of debt issuance costs by requiring debt issuance costs to be presented on the balance sheet as a direct deduction from the carrying amount of the associated debt liability, consistent with the presentation of debt discounts. Because this guidance did not address the treatment of debt issuance costs related to line-of-credit arrangements, additional guidance was issued in August 2015 stating that an entity may defer and amortize debt issuance costs over the term of a line-of-credit arrangement, regardless of whether there are any related outstanding borrowings. The initial adoption of this guidance required Talen Energy to reclassify long-term debt issuance costs on the Balance Sheet from assets to long-term debt. During the first quarter of 2016, Talen Energy retrospectively adopted this guidance. The December 31, 2015 Balance Sheet reflects a reclassification of $17 million between "Other noncurrent assets" and "Long-term debt" for the implementation. Issuance costs related to line-of-credit arrangements remain deferred as a long-term asset and amortized over the life of the arrangement. Accounting for Revenue from Contracts with Customers In May 2014, the FASB issued accounting guidance that establishes a comprehensive new model for the recognition of revenue from contracts with customers. This model is based on the core principle that revenue should be recognized 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. In March 2016, the FASB issued guidance to clarify the implementation of principal versus agent considerations, and in April 2016, the FASB issued guidance to clarify the identification of performance obligations contained within the original standard. This guidance can be applied using either a full retrospective or modified retrospective transition method. In August 2015, the FASB issued guidance that defers the effective date of the standard by one year, which for public business entities, results in initial application of this guidance in annual reporting periods beginning after December 15, 2017 and interim periods within those years. Entities may early adopt the guidance as of the original effective date of the standard, which for public business entities is annual reporting periods beginning after December 15, 2016. Talen Energy expects to adopt this guidance effective January 1, 2018. Talen Energy is currently assessing the impact of adopting this guidance on its consolidated financial statements, as well as the transition method it will use. Reporting Uncertainties about an Entity's Ability to Continue as a Going Concern In August 2014, the FASB issued accounting guidance which will require management to assess, for each interim and annual period, whether there are conditions or events that raise substantial doubt about an entity's ability to continue as a going concern. Substantial doubt about an entity's ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date the financial statements are issued. When management identifies conditions or events that raise substantial doubt about an entity's ability to continue as a going concern, management is required to disclose information that enables users of the financial statements to understand the principal conditions or events that raised substantial doubt about the entity's ability to continue as a going concern and management's evaluation of the significance of those conditions or events. If substantial doubt about the entity's ability to continue as a going concern has been alleviated as a result of management's plan, the entity should disclose information that allows the users of the financial statements to understand those plans. If the substantial doubt about the entity's ability to continue as a going concern is not alleviated by management's plans, management's plans to mitigate the conditions or events that gave rise to the substantial doubt about the entity's ability to continue as a going concern should be disclosed, as well as a statement that there is substantial doubt the entity's ability to continue as a going concern within one year after the date the financial statements are issued. This guidance should be applied prospectively within the annual periods ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. Talen Energy will adopt this guidance for the annual period ending December 31, 2016 and the adoption of this guidance is not expected to have a significant impact on its consolidated financial statements. Recognition of Measurement of Financial Assets and Financial Liabilities In January 2016, the FASB issued accounting guidance that affects the accounting for equity investments, financial liabilities under the fair value option, and the disclosure requirements for financial instruments. This guidance generally requires entities to measure equity investments that are not accounted for under the equity method of accounting and do not result in consolidation at fair value and recognize any changes in fair value in net income. Entities may elect to record equity investments without readily determinable fair values at cost, less impairment, adjusted for observable price changes. The impairment model for equity investments subject to this election is a single-step qualitative assessment performed each quarter. For financial liabilities measured using the fair value option, changes in fair value related to instrument-specific credit risk to be presented separately within OCI. This guidance should generally be applied prospectively for financial statements issued for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. Early adoption is generally not permitted, although entities may early adopt the provision related to financial liabilities under the fair value option. Talen Energy expects to adopt this guidance effective January 1, 2018. Upon adoption, an entity will record a cumulative-effect adjustment to beginning retained earnings as of the beginning of the first reporting period in which the guidance is adopted, with the exception that the amendments related to equity securities with readily determined fair values should be applied prospectively. Talen Energy is currently assessing the impact of adopting this guidance on its consolidated financial statements, which may be significant for equity securities held in the NDT funds. Accounting for Leases In February 2016, the FASB issued accounting guidance that updates the accounting for leases. The updated guidance will require lessees to recognize assets and liabilities for the rights and obligations created by their leases with lease terms of more than 12 months. Consistent with current accounting guidance, the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance (similar to the current capital lease) or an operating lease. However, unlike current accounting guidance, which requires only capital leases to be recognized on the balance sheet, the new accounting guidance will require both types of leases to be recognized on the balance sheet. The new accounting guidance also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. The accounting by lessors will remain largely unchanged. However, the new accounting guidance contains some targeted improvements that are intended to align, where necessary, lessor accounting with the lessee accounting model and with the updated revenue recognition guidance issued in 2014 and discussed above. This guidance is effective for annual reporting periods beginning after December 15, 2018 and interim periods within those years. Early application is permitted. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply. These practical expedients relate to the identification and classification of leases that commenced before the effective date, initial direct costs for leases that commenced before the effective date, and the ability to use hindsight in evaluating lessee options to extend or terminate a lease or to purchase the underlying asset. An entity that elects to apply the practical expedients will, in effect, continue to account for leases that commence before the effective date in accordance with previous accounting guidance unless the lease is modified, except that lessees are required to recognize a right-of-use asset and a lease liability for all operating leases at each reporting date based on the present value of the remaining minimum rental payments that were tracked and disclosed under previous accounting guidance. Talen Energy is currently assessing the impact of adopting this guidance on its consolidated financial statements and expects to adopt this guidance effective January 1, 2019. Share-Based Payment Accounting In March 2016, the FASB issued accounting guidance that changes the accounting for certain aspects of share-based payments to employees. This guidance requires the income tax effects of awards to be recognized in the income statement when the awards vest or are settled. For interim reporting purposes, excess tax benefits and tax deficiencies will be accounted for as discrete items in the period in which they occur and are excluded from the estimated annual effective tax rate. These amendments are applied prospectively. Excess tax benefits will be presented as an operating activity on the statement of cash flows, and this amendment can be applied retrospectively or prospectively. In addition, the requirement that excess tax benefits be realized before companies can recognize them will be eliminated; and this amendment will be applied using a modified retrospective transition method with a cumulative effect adjustment in retained earnings for excess tax benefits that have not previously been recognized. The guidance also requires an assessment of the realizability of any deferred tax assets it records upon adoption as a result of recognizing excess tax benefits and a valuation allowance will be recorded in retained earnings, if necessary. The guidance will increase the amount an employer can withhold to cover income taxes on awards and still qualify for the liability exception for shares used to satisfy the employer’s statutory income tax withholding obligation.; the amendments related to outstanding liability awards at the date of adoption will be applied using a modified retrospective transition method, with a cumulative-effect adjustment to retained earnings. Cash paid to a tax authority when shares are withheld to satisfy its statutory income tax withholding obligation will be recorded as a financing activity on the statement of cash flows. Companies will have to elect how to account for forfeitures of share-based payments by either recognizing forfeitures of awards as they occur or estimating the number of awards expected to be forfeited and adjusting the estimate when it is likely to change, as is currently required. This election is required at the entity level using a modified retrospective transition method, with a cumulative-effect adjustment to retained earnings. This guidance is effective for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. Early adoption is permitted. Talen Energy is currently assessing the impact of adopting this guidance on its consolidated financial statements and expects to adopt this guidance effective January 1, 2017.
Fair Value Transfer	Transfers between levels are recognized at end-of-reporting-period values.
Master Netting Arrangements	Net derivative positions on the balance sheets are not offset against the right to reclaim cash collateral (a receivable) or the obligation to return cash collateral (a payable) under master netting arrangements.
Investments	Securities held by Talen Energy's NDT funds are classified as available-for-sale.

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.