Tennessee Valley Authority PARRS A 2029 (TVE) 10-Q 5 Feb 20 2020 Q1 Quarterly report Financial data

DEI Document

DEI Document - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Document Information [Line Items]
Other revenue	$ 46	$ 44
Defined Benefit Plan, Other Cost (Credit)	$ 65	$ 64
Entity Registrant Name	Tennessee Valley Authority
Entity Central Index Key	0001376986
Current Fiscal Year End Date	--09-30
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Type	10-Q
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	0
Entity Current Reporting Status	Yes
Entity Shell Company	false

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating revenues
Sales of Electricity	$ 2,532	$ 2,681
Other revenue	46	44
Revenues	2,578	2,725
Operating expenses
Fuel	423	441
Purchased power	219	297
Operating and maintenance	689	745
Depreciation and amortization	584	345
Tax equivalents	131	132
Total operating expenses	2,046	1,960
Operating income	532	765
Other income (expense), net	12	24
Defined Benefit Plan, Other Cost (Credit)	65	64
Interest expense
Interest expense	287	302
Net income (loss)	$ 192	$ 423

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (UNAUDITED) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Net income (loss)		$ 192	$ 423
Other comprehensive income (loss)
Net unrealized gain (loss) on cash flow hedges		76	(52)
Reclassification to earnings from cash flow hedges	[1]	(59)	18
Total other comprehensive income (loss)		17	(34)
Total comprehensive income (loss)		$ 209	$ 389
[1]	There were no amounts excluded from effectiveness testing for any of the periods presented. Based on forecasted foreign currency exchange rates, TVA expects to reclassify approximately $15 million of gains from AOCI to interest expense within the next 12 months to offset amounts anticipated to be recorded in interest expense related to exchange gain on the debt.

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Current assets
Cash and cash equivalents	$ 304	$ 299
Accounts receivable, net	1,427	1,739
Inventories, net	1,052	999
Regulatory assets	159	156
Other current assets	109	85
Total current assets	3,051	3,278
Property, plant, and equipment
Completed plant	63,247	62,944
Less accumulated depreciation	(31,895)	(31,384)
Net completed plant	31,352	31,560
Construction in progress	1,972	1,893
Nuclear fuel	1,582	1,534
Capital leases	143	146
Total property, plant, and equipment, net	35,049	35,133
Investment funds	3,163	2,968
Regulatory and other long-term assets
Regulatory assets	8,410	8,763
Operating Lease, Right-of-Use Asset	192	0
Other long-term assets	334	325
Total regulatory and other long-term assets	8,936	9,088
Total assets	50,199	50,467
Current liabilities
Accounts payable and accrued liabilities	1,668	1,812
Accrued interest	303	296
Current portion of leaseback obligations	40	40
Regulatory liabilities	137	150
Short-term debt, net	895	922
Current maturities of power bonds	1,029	1,030
Current maturities of long-term debt of variable interest entities	39	39
Current maturities of notes payable	22	23
Total current liabilities	4,133	4,312
Other liabilities
Post-retirement and post-employment benefit obligations	6,062	6,181
Asset retirement obligations	5,588	5,453
Operating Lease, Liability, Noncurrent	130
Operating Lease, Liability, Current	72	0
Other long-term liabilities	2,201	2,490
Leaseback obligations	223	223
Regulatory liabilities	1
Total other liabilities	14,204	14,347
Long-term debt, net
Long-term power bonds, net	18,941	19,094
Long-term debt of variable interest entities, net	1,089	1,089
Long-term notes payable	1
Total long-term debt, net	20,030	20,183
Total liabilities	38,367	38,842
Proprietary capital
Power program appropriation investment	258	258
Power program retained earnings	11,015	10,823
Total power program proprietary capital	11,273	11,081
Nonpower programs appropriation investment, net	554	556
Accumulated other comprehensive income (loss)	5	(12)
Total proprietary capital	11,832	11,625
Total liabilities and proprietary capital	$ 50,199	$ 50,467

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 327
Cash flows from operating activities
Net income (loss)	192	$ 423
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Depreciation and amortization (including amortization of debt issuance costs and premiums/discounts)	590	350
Amortization of nuclear fuel cost	93	81
Non-cash retirement benefit expense	81	79
Amortization of Regulatory Asset	(3)	(22)
Changes in current assets and liabilities
Accounts receivable, net	316	117
Inventories and other current assets, net	(88)	(67)
Accounts payable and accrued liabilities	(213)	(343)
Accrued interest	6	0
Pension contributions	(75)	(75)
Other, net	(61)	(85)
Net cash provided by operating activities	838	502
Cash flows from investing activities
Construction expenditures	(465)	(500)
Nuclear fuel expenditures	(117)	(97)
Loans and other receivables
Advances	(2)	0
Repayments	1	2
Other, net	(7)	(6)
Net cash used in investing activities	(590)	(601)
Long-term debt
Redemptions and repurchases of power bonds	(218)	(1,002)
Repayments of Other Long-term Debt	0	1
Short-term debt issues (redemptions), net	(27)	1,105
Payments on leases and leasebacks	(1)	(1)
Other, net	3	0
Net cash provided by (used in) financing activities	(243)	101
Net change in cash and cash equivalents	5	2
Cash and cash equivalents at end of period	304
Significant non-cash transactions
Accrued capital and nuclear fuel expenditures	$ 254	$ 372

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN PROPRIETARY CAPITAL (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Power Program Appropriation Investment	$ 258		$ 258
Power Program Retained Earnings	11,015		10,823
Nonpower Programs Appropriation Investment, Net	554		556
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges	5		(12)
Total Proprietary Capital	11,832	$ 10,670	11,625	$ 10,283
Net income (loss)	192	423
Total other comprehensive income (loss)	17	(34)
Return on power program appropriation investment	(2)	(2)
Power Program Appropriation Investment
Power Program Appropriation Investment	258	258	258	258
Net income (loss)	0	0
Total other comprehensive income (loss)	0	0
Return on power program appropriation investment	0	0
Power Program Retained Earnings
Power Program Retained Earnings	11,015	9,827	10,823	9,404
Net income (loss)	194	425
Total other comprehensive income (loss)	0	0
Return on power program appropriation investment	(2)	(2)
Nonpower Programs Appropriation Investment, Net
Nonpower Programs Appropriation Investment, Net	554	562	556	564
Net income (loss)	(2)	(2)
Total other comprehensive income (loss)	0	0
Return on power program appropriation investment	0	0
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges	5	23	$ (12)	$ 57
Net income (loss)	0	0
Total other comprehensive income (loss)	17	(34)
Return on power program appropriation investment	$ 0	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Nature of Operations and Summary of Significant Accounting Policies	Summary of Significant Accounting Policies General The Tennessee Valley Authority ("TVA") is a corporate agency and instrumentality of the United States ("U.S.") that was created in 1933 by federal legislation in response to a proposal by President Franklin D. Roosevelt. TVA was created to, among other things, improve navigation on the Tennessee River, reduce the damage from destructive flood waters within the Tennessee River system and downstream on the lower Ohio and Mississippi Rivers, further the economic development of TVA's service area in the southeastern U.S., and sell the electricity generated at the facilities TVA operates. Today, TVA operates the nation's largest public power system and supplies power in most of Tennessee, northern Alabama, northeastern Mississippi, and southwestern Kentucky and in portions of northern Georgia, western North Carolina, and southwestern Virginia to a population of nearly 10 million people. TVA also manages the Tennessee River, its tributaries, and certain shorelines to provide, among other things, year-round navigation, flood damage reduction, and affordable and reliable electricity. Consistent with these primary purposes, TVA also manages the river system and public lands to provide recreational opportunities, adequate water supply, improved water quality, cultural and natural resource protection, and economic development. The power program has historically been separate and distinct from the stewardship programs. It is required to be self-supporting from power revenues and proceeds from power financings, such as proceeds from the issuance of bonds, notes, or other evidences of indebtedness (collectively, "Bonds") . Although TVA does not currently receive congressional appropriations, it is required to make annual payments to the U.S. Department of the Treasury ("U.S. Treasury") as a return on the government's appropriation investment in TVA's power facilities (the "Power Program Appropriation Investment"). In the 1998 Energy and Water Development Appropriations Act, Congress directed TVA to fund essential stewardship activities related to its management of the Tennessee River system and nonpower or stewardship properties with power revenues in the event that there were insufficient appropriations or other available funds to pay for such activities in any fiscal year. Congress has not provided any appropriations to TVA to fund such activities since 1999. Consequently, during 2000, TVA began paying for essential stewardship activities primarily with power revenues, with the remainder funded with user fees and other forms of revenues derived in connection with those activities. The activities related to stewardship properties do not meet the criteria of an operating segment under accounting principles generally accepted in the United States of America ("GAAP") . Accordingly, these assets and properties are included as part of the power program, TVA's only operating segment. Power rates are established by the TVA Board of Directors (the "TVA Board") as authorized by the Tennessee Valley Authority Act of 1933, as amended (the "TVA Act"). The TVA Act requires TVA to charge rates for power that will produce gross revenues sufficient to provide funds for operation, maintenance, and administration of its power system; payments to states and counties in lieu of taxes ("tax equivalents") ; debt service on outstanding indebtedness; payments to the U.S. Treasury in repayment of and as a return on the Power Program Appropriation Investment; and such additional margin as the TVA Board may consider desirable for investment in system assets, retirement of outstanding Bonds in advance of maturity, additional reduction of the Power Program Appropriation Investment, and other purposes connected with TVA's business. TVA fulfilled its requirement to repay $1.0 billion of the Power Program Appropriation Investment with the 2014 payment; therefore, this item is no longer a component of rate setting. In setting TVA's rates, the TVA Board is charged by the TVA Act to have due regard for the primary objectives of the TVA Act, including the objective that power shall be sold at rates as low as are feasible. Rates set by the TVA Board are not subject to review or approval by any state or federal regulatory body. Fiscal Year TVA's fiscal year ends September 30. Years ( 2020 , 2019 , etc.) refer to TVA's fiscal years unless they are preceded by "CY," in which case the references are to calendar years. Cost-Based Regulation Since the TVA Board is authorized by the TVA Act to set rates for power sold to its customers, TVA is self-regulated. Additionally, TVA's regulated rates are designed to recover its costs. Based on current projections, TVA believes that rates, set at levels that will recover TVA's costs, can be charged and collected. As a result of these factors, TVA records certain assets and liabilities that result from the regulated ratemaking process that would not be recorded under GAAP for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred because such costs are probable of future recovery in customer rates. Regulatory liabilities generally represent obligations to make refunds to customers for previous collections for costs that are not likely to be incurred or deferral of gains that will be credited to customers in future periods. TVA assesses whether the regulatory assets are probable of future recovery by considering factors such as applicable regulatory changes, potential legislation, and changes in technology. Based on these assessments, TVA believes the existing regulatory assets are probable of recovery. This determination reflects the current regulatory and political environment and is subject to change in the future. If future recovery of regulatory assets ceases to be probable, or any of the other factors described above cease to be applicable, TVA would no longer be considered to be a regulated entity and would be required to write off these costs. All regulatory asset write-offs would be required to be recognized in earnings in the period in which future recovery ceases to be probable. Basis of Presentation TVA prepares its consolidated interim financial statements in conformity with GAAP for consolidated interim financial information. Accordingly, TVA's consolidated interim financial statements do not include all of the information and notes required by GAAP for annual financial statements. As such, they should be read in conjunction with the audited financial statements for the year ended September 30, 2019 , and the notes thereto, which are contained in TVA's Annual Report on Form 10-K/A for the year ended September 30, 2019 (the "Annual Report"). In the opinion of management, all adjustments (consisting of items of a normal recurring nature) considered necessary for fair presentation are included on the consolidated interim financial statements. The accompanying consolidated interim financial statements, which have been prepared in accordance with GAAP, include the accounts of TVA, wholly-owned direct subsidiaries, and variable interest entities ("VIE") of which TVA is the primary beneficiary. See Note 9 — Variable Interest Entities . Intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements requires TVA to estimate the effects of various matters that are inherently uncertain as of the date of the consolidated financial statements. Although the consolidated financial statements are prepared in conformity with GAAP, TVA is required to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the amounts of revenues and expenses reported during the reporting period. Each of these estimates varies in regard to the level of judgment involved and its potential impact on TVA's financial results. Estimates are considered critical either when a different estimate could have reasonably been used, or where changes in the estimate are reasonably likely to occur from period to period, and such use or change would materially impact TVA's financial condition, results of operations, or cash flows. Reclassifications Certain historical amounts have been reclassified in the accompanying consolidated financial statements to the current presentation. In the December 31, 2018, Consolidated Statements of Cash Flows, amounts previously reported as $(10) million of Accounts payable and accrued liabilities were reclassified to Other, net in cash flows from operating activities. Additionally, amounts previously reported as $(10) million of Prepayment credits applied to revenue were reclassified to Other, net in cash flows from operating activities. Cash, Cash Equivalents, and Restricted Cash Cash includes cash on hand, non-interest bearing cash, and deposit accounts. All highly liquid investments with original maturities of three months or less are considered cash equivalents. Cash and cash equivalents that are restricted, as to withdrawal or use under the terms of certain contractual agreements, are recorded in Other long-term assets on the Consolidated Balance Sheets. Restricted cash and cash equivalents includes cash held in trusts that are currently restricted for TVA economic development loans and for certain TVA environmental programs in accordance with agreements related to compliance with certain environmental regulations. See Note 19 — Contingencies and Legal Proceedings — Legal Proceedings — Environmental Agreements . The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported on the Consolidated Balance Sheets and Consolidated Statements of Cash Flows: Cash, Cash Equivalents, and Restricted Cash At December 31, 2019 At September 30, 2019 Cash and cash equivalents $ 304 $ 299 Restricted cash and cash equivalents included in Other long-term assets 23 23 Total cash, cash equivalents, and restricted cash $ 327 $ 322 Allowance for Uncollectible Accounts The allowance for uncollectible accounts reflects TVA's estimate of probable losses inherent in its accounts and loans receivable balances, excluding the EnergyRight ® loans receivable. TVA determines the allowance based on known accounts, historical experience, and other currently available information including events such as customer bankruptcy and/or a customer failing to fulfill payment arrangements after 90 days. It also reflects TVA's corporate credit department's assessment of the financial condition of customers and the credit quality of the receivables. The allowance for uncollectible accounts was less than $ 1 million at both December 31, 2019 , and September 30, 2019 , for accounts receivable. Additionally, loans receivable of $135 million and $ 131 million at December 31, 2019 , and September 30, 2019 , respectively, are included in Accounts receivable, net and Other long-term assets, for the current and long-term portions, respectively, and are reported net of allowances for uncollectible accounts of less than $ 1 million at both December 31, 2019 , and September 30, 2019 . Revenues TVA recognizes revenue from contracts with customers to depict the transfer of goods or services to customers in an amount to which the entity expects to be entitled in exchange for those goods or services. For the generation and transmission of electricity, this is generally at the time the power is delivered to a metered customer delivery point for the customer's consumption or distribution. As a result, revenues from power sales are recorded as electricity is delivered to customers. In addition to power sales invoiced and recorded during the month, TVA accrues estimated unbilled revenues for power sales provided to five customers whose billing date occurs prior to the end of the month. Exchange power sales are presented in the accompanying Consolidated Statements of Operations as a component of sales of electricity. Exchange power sales are sales of excess power after meeting TVA native load and directly served requirements. Native load refers to the customers on whose behalf a company, by statute, franchise, regulatory requirement, or contract, has undertaken an obligation to serve. TVA engages in other arrangements in addition to power sales. Certain other revenue from activities related to TVA's overall mission are recorded in Other revenue. Revenues that are not related to the overall mission are recorded in Other income (expense), net. Leases TVA recognizes a lease asset and lease liability for leases with terms of greater than 12 months. Lease assets represent TVA's right to use an underlying asset for the lease term, and lease liabilities represent TVA's obligation to make lease payments arising from the lease, both of which are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. TVA has certain lease agreements that include variable lease payments that are based on energy production levels. These variable lease payments are not included in the measurement of the lease assets or lease liabilities but are recognized in the period in which the expenses are incurred. While not specifically structured as leases, certain power purchase agreements are deemed to contain a lease of the underlying generating units when the terms convey the right to control the use of the assets. Amounts recorded for these leases are generally based on the amount of the scheduled capacity payments due over the remaining terms of the purchased power agreements, the terms of which are approximately four years. The total lease obligation included in Operating lease liabilities related to these agreements is $ 130 million at December 31, 2019. TVA has agreements with lease and non-lease components and has elected to account for the components separately. Consideration is allocated to lease and non-lease components generally based on relative standalone selling prices. TVA has lease agreements which include options for renewal and early termination. The intent to renew a lease varies depending on the lease type and asset. Renewal options that are reasonably certain to be exercised are included in the lease measurements. The decision to terminate a lease early is dependent on various economic factors. No termination options have been included in TVA's lease measurements. Leases with an initial term of 12 months or less, which do not include an option to extend the initial term of the lease to greater than 12 months that TVA is reasonably certain to exercise, are not recorded on the Consolidated Balance Sheets at December 31, 2019 . Operating leases are recognized on a straight line basis over the term of the lease agreement. Rent expense associated with short-term leases and variable leases is recorded in Operating and maintenance expense, Fuel expense, or Purchased power expense on the Consolidated Statements of Operations. Expenses associated with finance leases result in the separate presentation of interest expense on the lease liability and amortization expense of the related lease asset on the Consolidated Statements of Operations. Depreciation TVA accounts for depreciation of its properties using the composite depreciation convention of accounting. Under the composite method, assets with similar economic characteristics are grouped and depreciated as one asset. Depreciation is generally computed on a straight-line basis over the estimated service lives of the various classes of assets. The estimation of asset useful lives requires management judgment, supported by external depreciation studies of historical asset retirement experience. Depreciation rates are determined based on the external depreciation studies. These studies are updated at least every five years. Depreciation expense was $539 million and $308 million for the three months ended December 31, 2019 and 2018 , respectively. See Note 5 — Plant Closures for a discussion of the impact of plant closures.

Impact of New Accounting Standa

Impact of New Accounting Standards and Interpretations	3 Months Ended
	Dec. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Impact of New Accounting Standards and Interpretations	The following are accounting standard updates issued by the Financial Accounting Standards Board ("FASB") that TVA adopted during 2020: Lease Accounting Description This guidance changes the provisions of recognition in both the lessee and lessor accounting models. The standard requires entities that lease assets ("lessees") to recognize on the balance sheet the assets and liabilities for the rights and obligations created by leases with terms of more than 12 months, while also refining the definition of a lease. In addition, lessees are required to disclose key information about the amount, timing, and uncertainty of cash flows arising from leasing arrangements. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily depend on its classification as a finance lease (formerly referred to as capital lease) or operating lease. The standard requires both types of leases to be recognized on the balance sheet. Operating leases will result in straight-line expense, while finance leases will result in recognition of interest on the lease liability separate from amortization expense. The accounting rules for the owner of assets leased by the lessee ("lessor accounting") remain relatively unchanged. The standard allows for certain practical expedients to be elected related to lease term determination, separation of lease and non-lease elements, reassessment of existing leases, and short-term leases. The standard is to be applied using a modified retrospective transition. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters TVA has elected the modified retrospective method of adoption effective October 1, 2019. Under the modified retrospective method of adoption, prior year reported results are not restated. TVA recorded $205 million and $210 million of lease assets and lease liabilities, respectively, for operating leases in effect at the adoption date. The accounting for finance leases remained substantially unchanged. Adoption of the standard did not materially impact results of operations or cash flows. TVA has elected to apply the following practical expedients: Practical Expedient Description Package of transition practical expedients (for leases commenced prior to adoption date; expedients must be adopted as a package) Do not need to (1) reassess whether any expired or existing contracts are leases or contain leases, (2) reassess the lease classification for any expired or existing leases, or (3) reassess initial direct costs for any existing leases. Short-term lease expedient (elect by class of underlying asset) Elect as an accounting policy to not apply the recognition requirements to short-term leases by asset class. Existing and expired land easements not previously accounted for as leases Elect to not evaluate existing or expired easements under the new guidance and carry forward current accounting treatment. Comparative reporting requirements for initial adoption Elect to apply transition requirements at adoption date, recognize cumulative effect adjustment to retained earnings in period of adoption, and not apply the new requirements to comparative periods, including disclosures. Derivatives and Hedging - Improvements to Accounting for Hedging Activities Description This guidance better aligns an entity's risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. To meet that objective, the amendments expand and refine hedge accounting for both nonfinancial and financial risk components and align the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters TVA has adopted the standard on a prospective basis. The adoption of this standard did not have a material impact on TVA's financial condition, results of operations, or cash flows. TVA only uses hedge accounting under its foreign currency swap arrangements, and the adoption of this standard has no impact on those arrangements. Customer's Accounting for Implementation Costs in a Cloud Arrangement That Is a Service Contract Description This guidance relates to the accounting for a customer's implementation costs in a hosting arrangement that is a service contract. The amendments align the requirements for capitalizing those implementation costs with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software and hosting arrangements that include an internal-use software license. The amendments also provide requirements for the classification of the capitalized costs and related expense and cash flows in the financial statements, the application of impairment guidance to the capitalized costs, and the application of abandonment guidance to the capitalized costs. Entities are required to apply the amendments either retrospectively or prospectively to all implementation costs incurred after the adoption date. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters Adoption of this standard did not have a material impact on TVA's financial condition, results of operation, or cash flows. TVA records qualified implementation costs in a cloud arrangement that is a service contract as a prepaid asset and amortizes the prepaid asset to Operating and maintenance expense based on the term of the contract. The following accounting standards have been issued but at December 31, 2019 , were not effective and had not been adopted by TVA: Financial Instruments - Credit Losses Description This guidance eliminates the probable initial recognition threshold in current GAAP and, instead, requires an allowance to be recorded for all expected credit losses for certain financial assets that are not measured at fair value. The allowance for credit losses is based on historical information, current conditions, and reasonable and supportable forecasts. The new standard also makes revisions to the other than temporary impairment model for available-for-sale debt securities. Disclosures of credit quality indicators in relation to the amortized cost of financing receivables are further disaggregated by year of origination. Effective Date for TVA The new standard is effective for TVA's interim and annual reporting periods beginning October 1, 2020. While early adoption is permitted, TVA does not plan to adopt the standard early. Effect on the Financial Statements or Other Significant Matters TVA is working to develop a model to calculate the allowance for credit losses based on management's estimate of the losses expected to be incurred over the life of the asset. TVA is evaluating the potential impact of the changes on its consolidated financial statements and related disclosures. Fair Value Measurement Disclosure Description The guidance changes certain disclosure requirements for fair value measurements. It removes certain disclosure requirements, such as the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; the policy for timing of the transfers between levels; and the valuation processes for Level 3 fair value measurements. Some disclosure requirements are added, such as the change in unrealized gains and losses included in other comprehensive income for recurring Level 3 fair value measurements and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Effective Date for TVA The new standard is effective for TVA's interim and annual reporting periods beginning October 1, 2020. While early adoption is permitted, TVA does not plan to adopt the standard early. Effect on the Financial Statements or Other Significant Matters TVA does not expect the adoption of this standard to have a material impact on TVA's financial condition, results of operations, or cash flows. TVA is evaluating the potential impact on related disclosures.

Accounts Receivable, Net

Accounts Receivable, Net	3 Months Ended
	Dec. 31, 2019
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Accounts Receivable, Net	Accounts Receivable, Net Accounts receivable primarily consist of amounts due from customers for power sales. The table below summarizes the types and amounts of TVA's accounts receivable: Accounts Receivable, Net At December 31, 2019 At September 30, 2019 Power receivables $ 1,326 $ 1,624 Other receivables 101 115 Accounts receivable, net (1) $ 1,427 $ 1,739 Note (1) Allowance for uncollectible accounts was less than $ 1 million at December 31, 2019 and September 30, 2019 , and therefore is not represented in the table above.

Inventories, Net

Inventories, Net	3 Months Ended
	Dec. 31, 2019
Inventory, Net [Abstract]
Inventories, Net	Inventories, Net The table below summarizes the types and amounts of TVA's inventories: Inventories, Net At December 31, 2019 At September 30, 2019 Materials and supplies inventory $ 752 $ 742 Fuel inventory 337 294 Renewable energy certificates/emission allowance inventory, net 17 16 Allowance for inventory obsolescence (54 ) (53 ) Inventories, net $ 1,052 $ 999

Other Long-Term Assets

Other Long-Term Assets	3 Months Ended
	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Long-Term Assets	Other Long-Term Assets The table below summarizes the types and amounts of TVA's other long-term assets: Other Long-Term Assets At December 31, 2019 At September 30, 2019 Loans and other long-term receivables, net $ 129 $ 125 EnergyRight ® receivables 78 81 Prepaid long-term service agreements (1) 29 22 Restricted cash and cash equivalents 23 23 Prepaid capacity payments 17 19 Other 58 55 Total other long-term assets $ 334 $ 325 Note (1) Certain amounts have been reclassified to conform with current year presentation. In association with the EnergyRight ® Solutions program, TVA's local power company customers ("LPCs") offer financing to end-use customers for the purchase of energy-efficient equipment. Depending on the nature of the energy-efficiency project, loans may have a maximum term of five years or 10 years . TVA purchases the resulting loans receivable from its LPCs. The loans receivable are then transferred to a third-party bank with which TVA has agreed to repay in full any loans receivable that have been in default for 180 days or more or that TVA has determined are uncollectible. Given this continuing involvement, TVA accounts for the transfer of the loans receivable as secured borrowings. The current and long-term portions of the loans receivable are reported in Accounts receivable, net and Other long-term assets, respectively, on TVA's Consolidated Balance Sheets. At December 31, 2019 , and September 30, 2019 , the carrying amount of the loans receivable, net of discount, reported in Accounts receivable, net was $ 20 million . See Note 10 — Other Long-Term Liabilities for information regarding the associated financing obligation. Prepaid Long-Term Service Agreements . TVA has entered into various long-term service agreements for major maintenance activities at certain of its combined cycle plants. TVA uses the direct expense method of accounting for these arrangements. TVA accrues for parts when it takes ownership and for contractor services when they are rendered. Under certain of these agreements, payments made exceed the value of parts received and services rendered. The current and long-term portions of the resulting prepayments are reported in Other current assets and Other long-term assets, respectively, on TVA's Consolidated Balance Sheets. At December 31, 2019, and September 30, 2019, prepayments of $7 million and $5 million , respectively, were recorded in Other current assets.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	3 Months Ended
	Dec. 31, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities Regulatory assets generally represent incurred costs that have been deferred because such costs are probable of future recovery in customer rates. Regulatory liabilities generally represent obligations to make refunds to customers for previous collections for costs that are not likely to be incurred or deferral of gains that will be credited to customers in future periods. Components of regulatory assets and regulatory liabilities are summarized in the table below: Regulatory Assets and Liabilities (1) At December 31, 2019 At September 30, 2019 Current regulatory assets Unrealized losses on interest rate derivatives $ 89 $ 89 Unrealized losses on commodity derivatives 49 39 Fuel cost adjustment receivable 21 28 Total current regulatory assets 159 156 Non-current regulatory assets Deferred pension costs and other post-retirement benefits costs 4,678 4,756 Non-nuclear decommissioning costs 1,725 1,741 Nuclear decommissioning costs 765 868 Unrealized losses on interest rate derivatives 1,074 1,241 Unrealized losses on commodity contracts 17 15 Other non-current regulatory assets 151 142 Total non-current regulatory assets 8,410 8,763 Total regulatory assets $ 8,569 $ 8,919 Current regulatory liabilities Fuel cost adjustment tax equivalents $ 134 $ 138 Unrealized gains on commodity derivatives 3 12 Total current regulatory liabilities $ 137 $ 150 Note (1) Amounts for Non-current regulatory liabilities were less than $1 million at December 31, 2019 and September 30, 2019, and are therefore not represented in the table above.

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Dec. 31, 2019
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entities	Variable Interest Entities A VIE is an entity that either (i) has insufficient equity to permit the entity to finance its activities without additional subordinated financial support or (ii) has equity investors who lack the characteristics of owning a controlling financial interest. When TVA determines that it has a variable interest in a VIE, a qualitative evaluation is performed to assess which interest holders have the power to direct the activities that most significantly impact the economic performance of the entity and have the obligation to absorb losses or receive benefits that could be significant to the entity. The evaluation considers the purpose and design of the business, the risks that the business was designed to create and pass along to other entities, the activities of the business that can be directed and which party can direct them, and the expected relative impact of those activities on the economic performance of the business through its life. TVA has the power to direct the activities of an entity when it has the ability to make key operating and financing decisions, including, but not limited to, capital investment and the issuance of debt. Based on the evaluation of these criteria, TVA has determined it is the primary beneficiary of certain entities and as such is required to account for the VIEs on a consolidated basis. John Sevier VIEs In 2012, TVA entered into a $1.0 billion construction management agreement and lease financing arrangement with John Sevier Combined Cycle Generation LLC ("JSCCG") for the completion and lease by TVA of the John Sevier Combined Cycle Facility ("John Sevier CCF") . JSCCG is a special single-purpose limited liability company formed in January 2012 to finance the John Sevier CCF through a $900 million secured note issuance (the "JSCCG notes") and the issuance of $100 million of membership interests subject to mandatory redemption. The membership interests were purchased by John Sevier Holdco LLC ("Holdco") . Holdco is a special single-purpose entity, also formed in January 2012, established to acquire and hold the membership interests in JSCCG. A non-controlling interest in Holdco is held by a third party through nominal membership interests, to which none of the income, expenses, and cash flows are allocated. The membership interests held by Holdco in JSCCG were purchased with proceeds from the issuance of $100 million of secured notes (the "Holdco notes") and are subject to mandatory redemption pursuant to a schedule of amortizing, semi-annual payments due each January 15 and July 15, with a final payment due in January 2042. The payment dates for the mandatorily redeemable membership interests are the same as those of the Holdco notes. The sale of the JSCCG notes, the membership interests in JSCCG, and the Holdco notes closed in January 2012. The JSCCG notes are secured by TVA's lease payments, and the Holdco notes are secured by Holdco's investment in, and amounts receivable from, JSCCG. TVA's lease payments to JSCCG are equal to and payable on the same dates as JSCCG's and Holdco's semi-annual debt service payments. In addition to the lease payments, TVA pays administrative and miscellaneous expenses incurred by JSCCG and Holdco. Certain agreements related to this transaction contain default and acceleration provisions. Due to its participation in the design, business conduct, and credit and financial support of JSCCG and Holdco, TVA has determined that it has a variable interest in each of these entities. Based on its analysis, TVA has concluded that it is the primary beneficiary of JSCCG and Holdco and, as such, is required to account for the VIEs on a consolidated basis. Holdco's membership interests in JSCCG are eliminated in consolidation. Southaven VIE In 2013, TVA entered into a $400 million lease financing arrangement with Southaven Combined Cycle Generation LLC ("SCCG") for the lease by TVA of the Southaven Combined Cycle Facility ("Southaven CCF") . SCCG is a special single-purpose limited liability company formed in June 2013 to finance the Southaven CCF through a $360 million secured notes issuance (the "SCCG notes") and the issuance of $40 million of membership interests subject to mandatory redemption. The membership interests were purchased by Southaven Holdco LLC ("SHLLC") . SHLLC is a special single-purpose entity, also formed in June 2013, established to acquire and hold the membership interests in SCCG. A non-controlling interest in SHLLC is held by a third party through nominal membership interests, to which none of the income, expenses, and cash flows of SHLLC are allocated. The membership interests held by SHLLC were purchased with proceeds from the issuance of $ 40 million of secured notes (the "SHLLC notes") and are subject to mandatory redemption pursuant to a schedule of amortizing, semi-annual payments due each February 15 and August 15, with a final payment due on August 15, 2033. The payment dates for the mandatorily redeemable membership interests are the same as those of the SHLLC notes, and the payment amounts are sufficient to provide returns on, as well as returns of, capital until the investment has been repaid to SHLLC in full. The rate of return on investment to SHLLC is 7.0 percent , which is reflected as interest expense on the Consolidated Statements of Operations. SHLLC is required to pay a pre-determined portion of the return on investment to Seven States Southaven, LLC ("SSSL") on each lease payment date as agreed in SHLLC's formation documents (the "Seven States Return"). The current and long-term portions of the Membership interests of VIE subject to mandatory redemption are included in Accounts payable and accrued liabilities and Other long-term liabilities, respectively. The payment dates for the mandatorily redeemable membership interests are the same as those of the SHLLC notes. The SCCG notes are secured by TVA's lease payments, and the SHLLC notes are secured by SHLLC's investment in, and amounts receivable from, SCCG. TVA's lease payments to SCCG are payable on the same dates as SCCG's and SHLLC's semi-annual debt service payments and are equal to the sum of (i) the amount of SCCG's semi-annual debt service payments, (ii) the amount of SHLLC's semi-annual debt service payments, and (iii) the amount of the Seven States Return. In addition to the lease payments, TVA pays administrative and miscellaneous expenses incurred by SCCG and SHLLC. Certain agreements related to this transaction contain default and acceleration provisions. In the event that TVA were to choose to exercise an early buy out feature of the Southaven facility lease, in part or in whole, TVA must pay to SCCG amounts sufficient for SCCG to repay or partially repay on a pro rata basis the membership interests held by SHLLC, including any outstanding investment amount plus accrued but unpaid return. TVA also has the right, at any time and without any early redemption of the other portions of the Southaven facility lease payments due to SCCG, to fully repay SHLLC's investment, upon which repayment SHLLC will transfer the membership interests to a designee of TVA. TVA participated in the design, business conduct, and financial support of SCCG and has determined that it has a direct variable interest in SCCG resulting from risk associated with the value of the Southaven CCF at the end of the lease term. Based on its analysis, TVA has determined that it is the primary beneficiary of SCCG and, as such, is required to account for the VIE on a consolidated basis. Impact on Consolidated Financial Statements The financial statement items attributable to carrying amounts and classifications of JSCCG, Holdco, and SCCG at December 31, 2019 , and September 30, 2019 , as reflected on the Consolidated Balance Sheets, are as follows: Summary of Impact of VIEs on Consolidated Balance Sheets At December 31, 2019 At September 30, 2019 Current liabilities Accrued interest $ 24 $ 11 Accounts payable and accrued liabilities 3 3 Current maturities of long-term debt of variable interest entities 39 39 Total current liabilities 66 53 Other liabilities Other long-term liabilities 25 25 Long-term debt, net Long-term debt of variable interest entities, net 1,089 1,089 Total liabilities $ 1,180 $ 1,167 Interest expense of $ 14 million related to debt of VIEs and membership interests of VIEs subject to mandatory redemption is included on the Consolidated Statements of Operations for both the three months ended December 31, 2019 and 2018 . Creditors of the VIEs have no recourse to the general credit of TVA. TVA does not have any obligations to provide financial support to the VIEs other than as prescribed in the terms of the agreements related to these transactions.

Other Long-Term Liabilities

Other Long-Term Liabilities	3 Months Ended
	Dec. 31, 2019
Other Liabilities, Noncurrent [Abstract]
Other Long-Term Liabilities	Other Long-Term Liabilities Other long-term liabilities consist primarily of liabilities related to certain derivative agreements, liabilities for environmental remediation, and liabilities under agreements related to compliance with certain environmental regulations. The table below summarizes the types and amounts of Other long-term liabilities: Other Long-Term Liabilities At December 31, 2019 At September 30, 2019 Interest rate swap liabilities $ 1,477 $ 1,676 Finance lease liabilities 180 182 Currency swap liabilities 120 193 EnergyRight ® financing obligation 88 90 Paradise pipeline financing obligation 79 80 Accrued long-term service agreement 61 66 Other 196 203 Total other long-term liabilities $ 2,201 $ 2,490 Interest Rate Swap Liabilities. TVA uses interest rate swaps to fix variable short-term debt to a fixed rate. The values of these derivatives are included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. At December 31, 2019 , and September 30, 2019 , the carrying amount of the interest rate swap liabilities reported in Accounts payable and accrued liabilities was $89 million and $88 million , respectively. See Note 14 — Risk Management Activities and Derivative Transactions — Derivatives Not Receiving Hedge Accounting Treatment — Interest Rate Derivatives for information regarding the interest rate swap liabilities. As of December 31, 2019 , interest rate swap liabilities decreased $199 million as compared to September 30, 2019 , primarily due to favorable changes in interest rates resulting in lower mark-to-market values on future expected net cash flows. EnergyRight ® Financing Obligation . TVA purchases certain loans receivable from its LPCs in association with the EnergyRight ® Solutions program. The current and long-term portions of the resulting financing obligation are reported in Accounts payable and accrued liabilities and Other long-term liabilities, respectively, on TVA's Consolidated Balance Sheets. At December 31, 2019 , and September 30, 2019 , the carrying amount of the financing obligation reported in Accounts payable and accrued liabilities was $22 million and $ 23 million , respectively. See Note 7 — Other Long-Term Assets for information regarding the associated loans receivable. Paradise Pipeline Financing Obligation. TVA reserves firm pipeline capacity on an approximately 19 mile pipeline owned by Texas Gas, which serves TVA's Paradise Combined Cycle Plant. The capacity contract contains a lease component due to TVA's exclusive right to use the pipeline. TVA accounts for this lease component as a financing transaction. The current and long-term portions of the resulting financing obligation are reported in Accounts payable and accrued liabilities and Other long-term liabilities, respectively, on TVA's Consolidated Balance Sheets. At both December 31, 2019 , and September 30, 2019 , related liabilities of less than $1 million were recorded in Accounts payable and accrued liabilities. Accrued Long-Term Service Agreement. TVA has entered into various long-term service agreements for major maintenance activities at certain of its combined cycle plants. TVA uses the direct expense method of accounting for these arrangements. TVA accrues for parts when it takes ownership and for contractor services when they are rendered. Under certain of these agreements, parts received and services rendered exceed payments made. The current and long-term portions of the resulting obligation are reported in Accounts payable and accrued liabilities and Other long-term liabilities, respectively, on TVA's Consolidated Balance Sheets. At December 31, 2019 , and September 30, 2019 , related liabilities of $ 14 million and $ 12 million , respectively, were recorded in Accounts payable and accrued liabilities.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations During the three months ended December 31, 2019 , TVA's total asset retirement obligations ("ARO") liability increased $135 million as a result of periodic accretion and revisions in estimate, partially offset by settlement projects that were conducted during the period. The nuclear and non-nuclear accretion amounts were deferred as regulatory assets. During the three months ended December 31, 2019 , $42 million of the related regulatory assets were amortized into expense as these amounts were collected in rates. See Note 8 — Regulatory Assets and Liabilities . TVA maintains investment trusts to help fund its decommissioning obligations. See Note 15 — Fair Value Measurements — Investment Funds and Note 19 — Contingencies and Legal Proceedings — Decommissioning Costs for a discussion of the trusts' objectives and the current balances of the trusts. Asset Retirement Obligation Activity (1) Nuclear Non-Nuclear Total Balance at September 30, 2019 $ 3,136 $ 2,480 $ 5,616 Settlements — (32 ) (32 ) Revisions in estimate — 117 117 Accretion (recorded as regulatory asset) 35 15 50 Balance at December 31, 2019 $ 3,171 $ 2,580 $ 5,751 Note (1) The current portion of ARO in the amount of $163 million at both December 31, 2019 , and September 30, 2019 , is included in Accounts payable and accrued liabilities. The revisions in non-nuclear estimates increased $ 117 million for the three months ended December 31, 2019 . In November 2019, the Tennessee Department of Environment and Conservation ("TDEC") released amendments to its regulations which govern solid waste disposal facilities, including TVA's active Coal Combustion Residuals ("CCR") facilities covered by a solid waste disposal permit and those which closed pursuant to a TDEC approved closure plan. Such facilities are generally subject to a 30-year post-closure care period during which the owner or operator must undertake certain activities, including monitoring and maintaining the facility. The amendments will, among other things, add an additional 50-year period after the end of the post-closure care period, require TVA to submit recommendations as to what activities must be performed during this 50-year period to protect human health and the environment, and require TVA to submit revised closure plans every 10 years. This regulatory revision resulted in an increase of $129 million , of which $38 million was related to operating CCR facilities and $91 million was related to inactive or closed CCR facilities.

Debt and Other Obligations

Debt and Other Obligations	3 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt and Other Obligations	Debt and Other Obligations Debt Outstanding Total debt outstanding at December 31, 2019 , and September 30, 2019 , consisted of the following: Debt Outstanding At December 31, 2019 At September 30, 2019 Short-term debt Short-term debt, net $ 895 $ 922 Current maturities of power bonds issued at par 1,029 1,030 Current maturities of long-term debt of VIEs issued at par 39 39 Current maturities of notes payable 22 23 Total current debt outstanding, net 1,985 2,014 Long-term debt Long-term power bonds (1) 19,065 19,225 Long-term debt of variable interest entities, net 1,089 1,089 Unamortized discounts, premiums, issue costs, and other (124 ) (131 ) Total long-term debt, net 20,030 20,183 Total outstanding debt $ 22,015 $ 22,197 Note (1) Includes net exchange gain from currency transactions of $133 million and $191 million at December 31, 2019 , and September 30, 2019 , respectively. Debt Securities Activity The table below summarizes the long-term debt securities activity for the period from October 1, 2019, to December 31, 2019 : Debt Securities Activity (1) Date Amount (2) Interest Rate Redemptions/Maturities electronotes ® First Quarter 2020 $ 217 3.33 % 2009 Series B December 2019 1 3.77 % Total redemptions/maturities of debt $ 218 Note (1) Amounts for notes payable were less than $1 million at December 31, 2019, and are therefore not represented in the table above. (2) All redemptions were at 100 percent of par. Credit Facility Agreements TVA and the U.S. Treasury, pursuant to the TVA Act, have entered into a memorandum of understanding under which the U.S. Treasury provides TVA with a $ 150 million credit facility. This credit facility was renewed in 2019 with a maturity date of September 30, 2020 . Access to this credit facility or other similar financing arrangements with the U.S. Treasury has been available to TVA since the 1960s. TVA can borrow under the U.S. Treasury credit facility only if it cannot issue Bonds in the market on reasonable terms, and TVA considers the U.S. Treasury credit facility a secondary source of liquidity. The interest rate on any borrowing under this facility is based on the average rate on outstanding marketable obligations of the U.S. with maturities from date of issue of one year or less. There were no outstanding borrowings under the facility at December 31, 2019 . The availability of this credit facility may be impacted by how the U.S. government addresses the possibility of approaching its debt limit. TVA also has funding available under four long-term revolving credit facilities totaling $ 2.7 billion : a $150 million credit facility that matures on December 11, 2021, a $ 500 million credit facility that matures on February 1, 2022, a $ 1.0 billion credit facility that matures on June 13, 2023, and a $ 1.0 billion credit facility that matures on September 28, 2023. The interest rate on any borrowing under these facilities varies based on market factors and the rating of TVA's senior unsecured, long-term, non-credit-enhanced debt. TVA is required to pay an unused facility fee on the portion of the total $ 2.7 billion that TVA has not borrowed or committed under letters of credit. This fee, along with letter of credit fees, may fluctuate depending on the rating of TVA's senior unsecured, long-term, non-credit-enhanced debt. At December 31, 2019 , and September 30, 2019 , there were approximately $1.2 billion and $ 1.3 billion , respectively, of letters of credit outstanding under these facilities, and there were no borrowings outstanding. See Note 14 — Risk Management Activities and Derivative Transactions — Other Derivative Instruments — Collateral . The following table provides additional information regarding TVA's funding available under the four long-term revolving credit facilities: Summary of Long-Term Credit Facilities At December 31, 2019 Maturity Date Facility Limit Letters of Credit Outstanding Cash Borrowings Availability December 2021 $ 150 $ 38 $ — $ 112 February 2022 500 500 — — June 2023 1,000 342 — 658 September 2023 1,000 310 — 690 Total $ 2,650 $ 1,190 $ — $ 1,460 Lease/Leasebacks TVA previously entered into leasing transactions to obtain third-party financing for 24 peaking combustion turbine units ("CTs") as well as certain qualified technological equipment and software ("QTE"). Due to TVA's continuing involvement with the combustion turbine facilities and the QTE during the leaseback term, TVA accounted for the lease proceeds as financing obligations. At both December 31, 2019 , and September 30, 2019 , the outstanding leaseback obligations related to the remaining CTs and QTE were $ 263 million . In March 2019, TVA made final rent payments under lease/leaseback transactions involving eight CTs, and TVA had previously acquired the equity interests related to these transactions. These transactions were terminated in July 2019. Final rent payments are scheduled to be made under the remaining CT lease/leaseback transactions on various dates from May 2020 to January 2022. TVA has already acquired the equity interests related to transactions involving eight of these CTs and will have the option to acquire the equity interests related to transactions involving the remaining eight CTs for additional amounts. In addition, on October 30, 2019, TVA provided notice of its intent to purchase the ownership interest in certain QTE. Repurchase payments are expected to be paid through a series of installments in 2021 and 2022, after which the associated leases will be terminated.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Accumulated other comprehensive income (loss) ("AOCI") represents market valuation adjustments related to TVA's currency swaps. The currency swaps are cash flow hedges and are the only derivatives in TVA's portfolio that have been designated and qualify for hedge accounting treatment. TVA records exchange rate gains and losses on its foreign currency-denominated debt and any related accrued interest in net income and marks its currency swap assets and liabilities to market through other comprehensive income (loss) ("OCI") . TVA then reclassifies an amount out of AOCI into net income, offsetting the exchange gain/loss recorded on the debt. During the three months ended December 31, 2019 and 2018 , TVA reclassified $ 59 million of gains and $18 million of losses, respectively, related to its cash flow hedges from AOCI to Interest expense. See Note 14 — Risk Management Activities and Derivative Transactions . TVA records certain assets and liabilities that result from the regulated ratemaking process that would not be recorded under GAAP for non-regulated entities. As such, certain items that would generally be reported in AOCI or that would impact the statements of operations are recorded as regulatory assets or regulatory liabilities. See Note 8 — Regulatory Assets and Liabilities for a schedule of regulatory assets and liabilities. See Note 14 — Risk Management Activities and Derivative Transactions for a discussion of the recognition in AOCI of gains and losses associated with certain derivative contracts. See Note 15 — Fair Value Measurements for a discussion of the recognition of certain investment fund gains and losses as regulatory assets and liabilities. See Note 18 — Benefit Plans for a discussion of the regulatory accounting related to components of TVA's benefit plans.

Risk Management Activities and

Risk Management Activities and Derivative Transactions	3 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Risk Management Activities and Derivative Transactions	Risk Management Activities and Derivative Transactions TVA is exposed to various risks. These include risks related to commodity prices, investment prices, interest rates, currency exchange rates, and inflation as well as counterparty credit and performance risks. To help manage certain of these risks, TVA has historically entered into various derivative transactions, principally commodity option contracts, forward contracts, swaps, swaptions, futures, and options on futures. Other than certain derivative instruments in its trust investment funds, it is TVA's policy to enter into these derivative transactions solely for hedging purposes and not for speculative purposes. TVA has suspended its Financial Trading Program ("FTP") and no longer uses financial instruments to hedge risks related to commodity prices; however, TVA plans to continue to manage fuel price volatility through other methods and to periodically reevaluate its suspended FTP program for future use of financial instruments. Overview of Accounting Treatment TVA recognizes certain of its derivative instruments as either assets or liabilities on its Consolidated Balance Sheets at fair value. The accounting for changes in the fair value of these instruments depends on (1) whether TVA uses regulatory accounting to defer the derivative gains and losses, (2) whether the derivative instrument has been designated and qualifies for hedge accounting treatment, and (3) if so, the type of hedge relationship (for example, cash flow hedge). The following tables summarize the accounting treatment that certain of TVA's financial derivative transactions receive: Summary of Derivative Instruments That Receive Hedge Accounting Treatment (part 1) Amount of Mark-to-Market Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss) Three Months Ended Derivatives in Cash Flow Hedging Relationship Objective of Hedge Transaction Accounting for Derivative 2019 2018 Currency swaps To protect against changes in cash flows caused by changes in foreign currency exchange rates (exchange rate risk) Unrealized gains and losses are recorded in AOCI and reclassified to interest expense to the extent they are offset by gains and losses on the hedged transaction $ 76 $ (52 ) Summary of Derivative Instruments That Receive Hedge Accounting Treatment (part 2) (1) Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income to Interest Expense Three Months Ended Derivatives in Cash Flow Hedging Relationship 2019 2018 Currency swaps $ 59 $ (18 ) Note (1) There were no amounts excluded from effectiveness testing for any of the periods presented. Based on forecasted foreign currency exchange rates, TVA expects to reclassify approximately $ 15 million of gains from AOCI to interest expense within the next 12 months to offset amounts anticipated to be recorded in interest expense related to exchange gain on the debt. Summary of Derivative Instruments That Do Not Receive Hedge Accounting Treatment Amount of Gain (Loss) Recognized in Income on Derivatives (1) Three Months Ended December 31 Derivative Type Objective of Derivative Accounting for Derivative Instrument 2019 2018 Interest rate swaps To fix short-term debt variable rate to a fixed rate (interest rate risk) Mark-to-Market gains and losses are recorded as regulatory assets or liabilities $ (21 ) $ (20 ) Commodity contract derivatives To protect against fluctuations in market prices of purchased coal or natural gas (price risk) Mark-to-market gains and losses are recorded as regulatory assets or liabilities Realized gains and losses due to contract settlements are recognized in fuel expense as incurred 1 — Note (1) All of TVA's derivative instruments that do not receive hedge accounting treatment have unrealized gains (losses) that would otherwise be recognized in income but instead are deferred as regulatory assets and liabilities. As such, there were no related gains (losses) recognized in income for these unrealized gains (losses) for the three months ended December 31, 2019 and 2018 . Fair Values of TVA Derivatives At December 31, 2019 At September 30, 2019 Derivatives That Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Currency swaps £200 million Sterling $ (69 ) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(64) $ (90 ) Accounts payable and £250 million Sterling (27 ) Accounts payable and accrued liabilities $(4); Other long-term liabilities $(23) (61 ) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(56) £150 million Sterling (36 ) Accounts payable and accrued liabilities $(3); Other long-term liabilities $(33) (57 ) Accounts payable and Derivatives That Do Not Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Interest rate swaps $1.0 billion notional $ (1,124 ) Accounts payable and $ (1,261 ) Accounts payable and $476 million notional (436 ) Accounts payable and (498 ) Accounts payable and $42 million notional (5 ) Accounts payable and (5 ) Accounts payable and Commodity contract derivatives (62 ) Other current assets $4; Accounts payable and accrued liabilities $(49); Other long-term liabilities $(17) (41 ) Other current assets $12; Accounts payable and accrued liabilities $(37); Other long-term liabilities $(16) Cash Flow Hedging Strategy for Currency Swaps To protect against exchange rate risk related to three British pound sterling denominated Bond transactions, TVA entered into foreign currency hedges at the time the Bond transactions occurre d. TVA had three currency swaps outstanding at December 31, 2019 , with total currency exposure of £600 million and expiration dates ranging fr om 2021 to 2043 . When the dollar strengthens against the British pound sterling, the exchange gain on the Bond liability and related accrued interest is offset by an equal amount of loss on the swap contract that is reclassified out of AOCI. Conversely, the exchange loss on the Bond liability and related accrued interest is offset by an equal amount of gain on the swap contract that is reclassified out of AOCI. All such exchange gains or losses on the Bond liability and related accrued interest are included in Long-term debt, net and Accounts payable and accrued liabilities, respectively. The offsetting exchange losses or gains on the swap contracts are recognized in AOCI. If any gain (loss) were to be incurred as a result of the early termination of the foreign currency swap contract, the resulting income (expense) would be amortized over the remaining life of the associated Bond as a component of Interest expense. The values of the currency swap liabilities are included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. Derivatives Not Receiving Hedge Accounting Treatment Interest Rate Derivatives . Generally TVA uses interest rate swaps to fix variable short-term debt to a fixed rate, and TVA uses regulatory accounting treatment to defer the mark-to-market ("MtM") gains and losses on its interest rate swaps. The net deferred unrealized gains and losses are classified as regulatory assets or liabilities on TVA's Consolidated Balance Sheets and are included in the ratemaking formula when gains or losses are realized. The values of these derivatives are included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets, and realized gains and losses, if any, are included on TVA's Consolidated Statements of Operations. For the three months ended December 31, 2019 and 2018 , the changes in fair market value of the interest rate swaps resulted in the deferral of unrealized gains of $171 million and unrealized losses of $110 million , respectively. Commodity Derivatives . TVA enters into certain derivative contracts for coal and natural gas that require physical delivery of the contracted quantity of the commodity. TVA marks to market all such contracts and defers the fair market values as regulatory assets or liabilities on a gross basis. At December 31, 2019 , TVA's coal and natural gas contract derivatives had terms of up to two and five years, respectively. Commodity Contract Derivatives At December 31, 2019 At September 30, 2019 Number of Contracts Notional Amount Fair Value (MtM) Number of Contracts Notional Amount Fair Value ( MtM ) Coal contract derivatives 9 10 million tons $ (16 ) 8 9 million tons $ (4 ) Natural gas contract derivatives 53 365 million mmBtu $ (46 ) 65 330 million mmBtu $ (37 ) Offsetting of Derivative Assets and Liabilities The amounts of TVA's derivative instruments as reported on the Consolidated Balance Sheets at December 31, 2019 , and September 30, 2019 , are shown in the table below: Derivative Assets and Liabilities (1) At December 31, 2019 At September 30, 2019 Assets Commodity derivatives not subject to master netting or similar arrangement $ 4 $ 12 Liabilities Currency swaps (2) $ 132 $ 208 Interest rate swaps (2) 1,565 1,764 Total derivatives subject to master netting or similar arrangement 1,697 1,972 Commodity derivatives not subject to master netting or similar arrangement 66 53 Total liabilities $ 1,763 $ 2,025 Notes (1) Offsetting amounts primarily include counterparty netting of derivative contracts, margin account deposits for futures commission merchants transactions, and cash collateral received or paid in accordance with the accounting guidance for derivatives and hedging transactions. There were no offsetting amounts on TVA's Consolidated Balance Sheets at either December 31, 2019 or September 30, 2019. (2) Letters of credit of approximately $1.2 billion and $ 1.3 billion were posted as collateral at December 31, 2019 , and September 30, 2019 , respectively, to partially secure the liability positions of one of the currency swaps and one of the interest rate swaps in accordance with the collateral requirements for these derivatives. Other Derivative Instruments Investment Fund Derivatives . Investment funds consist primarily of funds held in the Nuclear Decommissioning Trust ("NDT") , the Asset Retirement Trust ("ART") , the Supplemental Executive Retirement Plan ("SERP") , and the TVA Deferred Compensation Plan ("DCP"). See Note 15 — Fair Value Measurements — Investment Funds for a discussion of the trusts, plans, and types of investments. The NDT and ART may invest in derivative instruments which may include swaps, futures, options, forwards, and other instruments. At December 31, 2019 , and September 30, 2019 , the NDT held investments in forward contracts to purchase debt securities. The fair values of these derivatives were in net asset positions totaling $2 million and $22 million at December 31, 2019 , and September 30, 2019 , respectively. Collateral . TVA's interest rate swaps and currency swaps contain contract provisions that require a party to post collateral (in a form such as cash or a letter of credit) when the party's liability balance under the agreement exceeds a certain threshold. At December 31, 2019 , the aggregate fair value of all derivative instruments with credit-risk related contingent features that were in a liability position was $ 1.7 billion . TVA's collateral obligations at December 31, 2019 , under these arrangements were approximately $ 1.2 billion , for which TVA had posted approximately $ 1.2 billion in letters of credit. These letters of credit reduce the available balance under the related credit facilities. TVA's assessment of the risk of its nonperformance includes a reduction in its exposure under the contract as a result of this posted collateral. For all of its derivative instruments with credit-risk related contingent features: • If TVA remains a majority-owned U.S. government entity but Standard & Poor's Financial Services, LLC ("S&P") or Moody's Investors Service, Inc. ("Moody's") downgrades TVA's credit rating to AA or Aa2, respectively, TVA's collateral obligations would likely increase by $ 22 million , and • If TVA ceases to be majority-owned by the U.S. government, TVA's credit rating would likely be downgraded and TVA would be required to post additional collateral. Counterparty Risk TVA may be exposed to certain risks when a counterparty has the potential to fail to meet its obligations in accordance with agreed terms. These risks may be related to credit, operational, or nonperformance matters. To mitigate certain counterparty risk, TVA analyzes the counterparty's financial condition prior to entering into an agreement, establishes credit limits, monitors the appropriateness of those limits, as well as any changes in the creditworthiness of the counterparty, on an ongoing basis, and when required, employs credit mitigation measures, such as collateral or prepayment arrangements and master purchase and sale agreements, to mitigate credit risk. Customers . TVA is exposed to counterparty credit risk associated with trade accounts receivable from delivered power sales to LPCs, and from industries and federal agencies directly served, all located in the Tennessee Valley region. Of the $1.3 billion and $1.6 billion of receivables from power sales outstanding at December 31, 2019, and September 30, 2019, respectively, nearly all counterparties were rated investment grade. T VA is also exposed to risk from exchange power arrangements with a small number of investor-owned regional utilities related to either delivered power or the replacement of open positions of longer-term purchased power or fuel agreements. TVA believes its policies and procedures for counterparty performance risk reviews have generally protected TVA against significant exposure related to market and economic conditions. See Note 1 — Summary of Significant Accounting Policies — Allowance for Uncollectible Accounts and Note 3 — Accounts Receivable, Net . TVA had revenue from two LPCs that accounted for 16 percent of total operating revenue for the three months ended December 31, 2019 and 2018. Suppliers . If one of TVA's fuel or purchased power suppliers fails to perform under the terms of its contract with TVA, TVA might lose the money that it paid to the supplier under the contract and have to purchase replacement fuel or power on the spot market, perhaps at a significantly higher price than TVA was entitled to pay under the contract. In addition, TVA might not be able to acquire replacement fuel or power in a timely manner and thus might be unable to satisfy its own obligations to deliver power. Nuclear fuel requirements, including uranium mining and milling, conversion services, enrichment services, and fabrication services, are met from various suppliers, depending on the type of service. TVA purchases the majority of its natural gas requirements from a variety of suppliers under short-term contracts. To help ensure a reliable supply of coal, TVA had coal contracts with multiple suppliers at December 31, 2019 . The contracted supply of coal is sourced from multiple geographic regions of the U.S. and is to be delivered via various transportation methods (e.g., barge, rail, and truck). Emerging technologies, environmental regulations, and low natural gas prices have contributed to weak demand for coal. As a result, coal suppliers are facing increased financial pressure, which has led to relatively poor credit ratings and bankruptcies. Continued difficulties by coal suppliers could result in consolidations, additional bankruptcies, restructuring, contract renegotiations, or other scenarios. Under these scenarios and TVA's potential available responses, TVA does not anticipate a significant financial impact in obtaining continued fuel supply for its coal-fired generation. Nuclear fuel is obtained predominantly through long-term uranium concentrate supply contracts, contracted conversion services, contracted enrichment services, or a combination thereof, and contracted fuel fabrication services. The supply markets for uranium concentrates and certain nuclear fuel services are subject to price fluctuations and availability restrictions. Supply market conditions may make procurement contracts subject to credit risk related to the potential nonperformance of counterparties. In the event of nonperformance by these or other suppliers, TVA believes that replacement uranium concentrate can be obtained, although at prices that may be unfavorable when compared to the prices under the current supply agreements. TVA has a power purchase agreement that expires on March 31, 2032, with a supplier of electricity for 440 megawatts ("MW") of summer net capability from a lignite-fired generating plant. TVA has determined that the supplier has the equivalent of a non-investment grade credit rating; therefore, the supplier has provided credit assurance to TVA under the terms of the agreement. Derivative Counterparties . T VA has entered into physical and financial contracts that qualify as derivatives for hedging purposes, and TVA's NDT, ART, and qualified defined benefit pension plan have entered into derivative contracts for investment purposes. If a counterparty to one of the physical or financial derivative transactions defaults, TVA might incur substantial costs in connection with entering into a replacement transaction. If a counterparty to the derivative contracts into which the NDT, the ART, and the qualified pension plan have entered for investment purposes defaults, the value of the investment could decline significantly or perhaps become worthless. TVA has concentrations of credit risk from the banking, coal, and gas industries because multiple companies in these industries serve as counterparties to TVA in various derivative transactions. At December 31, 2019 , all of TVA's currency swaps and interest rate swaps as well as all of the derivatives in the NDT and ART were with banking counterparties whose Moody's credit ratings were A3 or higher. TVA classifies qualified forward coal and natural gas contracts as derivatives. See Derivatives Not Receiving Hedge Accounting Treatment above. At December 31, 2019 , the coal contracts were with counterparties whose Moody's credit rating, or TVA's internal analysis when such information was unavailable, ranged from D to Ba1 . At December 31, 2019 , the natural gas contracts were with counterparties whose ratings ranged from B3 to A2 . See Suppliers above for discussion of challenges facing the coal industry.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is determined based on the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the asset or liability's principal market, or in the absence of a principal market, the most advantageous market for the asset or liability in an orderly transaction between market participants. TVA uses market or observable inputs as the preferred source of values, followed by assumptions based on hypothetical transactions in the absence of market inputs. Valuation Techniques The measurement of fair value results in classification into a hierarchy by the inputs used to determine the fair value as follows: Level 1 — Unadjusted quoted prices in active markets accessible by the reporting entity for identical assets or liabilities. Active markets are those in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing. Level 2 — Pricing inputs other than quoted market prices included in Level 1 that are based on observable market data and that are directly or indirectly observable for substantially the full term of the asset or liability. These include quoted market prices for similar assets or liabilities, quoted market prices for identical or similar assets in markets that are not active, adjusted quoted market prices, inputs from observable data such as interest rate and yield curves, volatilities and default rates observable at commonly quoted intervals, and inputs derived from observable market data by correlation or other means. Level 3 — Pricing inputs that are unobservable, or less observable, from objective sources. Unobservable inputs are only to be used to the extent observable inputs are not available. These inputs maintain the concept of an exit price from the perspective of a market participant and should reflect assumptions of other market participants. An entity should consider all market participant assumptions that are available without unreasonable cost and effort. These are given the lowest priority and are generally used in internally developed methodologies to generate management's best estimate of the fair value when no observable market data is available. A financial instrument's level within the fair value hierarchy (where Level 1 is the highest and Level 3 is the lowest) is based on the lowest level of input significant to the fair value measurement. The following sections describe the valuation methodologies TVA uses to measure different financial instruments at fair value. Except for gains and losses on SERP and DCP assets, all changes in fair value of these assets and liabilities have been recorded as changes in regulatory assets, regulatory liabilities, or AOCI on TVA's Consolidated Balance Sheets and Consolidated Statements of Comprehensive Income (Loss). Except for gains and losses on SERP and DCP assets, there has been no impact to the Consolidated Statements of Operations or the Consolidated Statements of Cash Flows related to these fair value measurements. Investment Funds At December 31, 2019 , Investment funds were composed of $ 3.2 billion of equity securities and debt securities classified as trading measured at fair value. Equity and trading debt securities are held in the NDT, ART, SERP, and DCP. The NDT holds funds for the ultimate decommissioning of TVA's nuclear power plants. The ART holds funds primarily for the costs related to the future closure and retirement of TVA's other long-lived assets. The balances in the NDT and ART were $ 2.3 billion and $ 815 million , respectively, at December 31, 2019 . TVA established a SERP to provide benefits to selected employees of TVA which are comparable to those provided by competing organizations. The DCP is designed to provide participants with the ability to defer compensation until employment with TVA ends. The NDT, ART, SERP, and DCP funds are invested in portfolios of securities generally designed to achieve a return in line with overall equity and debt market performance. The NDT, ART, SERP, and DCP are composed of multiple types of investments and are managed by external institutional investment managers. Most U.S. and international equities, U.S. Treasury inflation-protected securities, real estate investment trust securities, and cash securities and certain derivative instruments are measured based on quoted exchange prices in active markets and are classified as Level 1 valuations. Fixed-income investments, high-yield fixed-income investments, currencies, and most derivative instruments are non-exchange traded and are classified as Level 2 valuations. These measurements are based on market and income approaches with observable market inputs. Private equity limited partnerships, private real asset investments, and private credit investments may include holdings of investments in private real estate, venture capital, buyout, mezzanine or subordinated debt, restructuring or distressed debt, and special situations through funds managed by third-party investment managers. These investments generally involve a three -to- four -year period where the investor contributes capital, followed by a period of distribution, typically over several years. The investment period is generally, at a minimum, 10 years or longer. The NDT had unfunded commitments related to private equity limited partnerships of $ 208 million , unfunded commitments related to private real assets of $ 57 million , and unfunded commitments related to private credit of $10 million at December 31, 2019 . The ART had unfunded commitments related to private equity limited partnerships of $103 million , unfunded commitments related to private real assets of $41 million , and unfunded commitments related to private credit of $5 million at December 31, 2019 . These investments have no redemption or limited redemption options and may also impose restrictions on the NDT's and ART's ability to liquidate their investments. There are no readily available quoted exchange prices for these investments. The fair value of these investments is based on information provided by the investment managers. These investments are valued on a quarterly basis. TVA's private equity limited partnerships, private real asset investments, and private credit investments are valued at net asset values ("NAV") as a practical expedient for fair value. TVA classifies its interest in these types of investments as investments measured at net asset value in the fair value hierarchy. Commingled funds represent investment funds comprising multiple individual financial instruments. The commingled funds held by the NDT, ART, SERP, and DCP consist of either a single class of securities, such as equity, debt, or foreign currency securities, or multiple classes of securities. All underlying positions in these commingled funds are either exchange traded or measured using observable inputs for similar instruments. The fair value of commingled funds is based on NAV per fund share (the unit of account), derived from the prices of the underlying securities in the funds. These commingled funds can be redeemed at the measurement date NAV and are classified as Commingled funds measured at net asset value in the fair value hierarchy. Realized and unrealized gains and losses on equity and trading debt securities are recognized in current earnings and are based on average cost. The gains and losses of the NDT and ART are subsequently reclassified to a regulatory asset or liability account in accordance with TVA's regulatory accounting policy. See Note 1 — Summary of Significant Accounting Policies — Cost-Based Regulation . TVA recorded unrealized gains and losses related to its equity and trading debt securities held during each period as follows: Unrealized Investment Gains (Losses) Three Months Ended Fund Financial Statement Presentation 2019 2018 NDT Regulatory asset $ 111 $ (201 ) ART Regulatory asset 37 (104 ) SERP Other income (expense) 1 (6 ) DCP Other income (expense) 1 (3 ) Currency and Interest Rate Derivatives See Note 14 — Risk Management Activities and Derivative Transactions — Cash Flow Hedging Strategy for Currency Swaps and Derivatives Not Receiving Hedge Accounting Treatment for a discussion of the nature, purpose, and contingent features of TVA's currency swaps and interest rate swaps. These swaps are classified as Level 2 valuations and are valued based on income approaches using observable market inputs for similar instruments. Commodity Contract Derivatives Most of these contracts are valued based on market approaches which utilize short- and mid-term market-quoted prices from an external industry brokerage service. A small number of these contracts are valued based on a pricing model using long-term price estimates from TVA's coal price forecast. To value the volume option component of applicable coal contracts, TVA uses a Black-Scholes pricing model which includes inputs from the forecast, contract-specific terms, and other market inputs. These contracts are classified as Level 3 valuations. Nonperformance Risk The assessment of nonperformance risk, which includes credit risk, considers changes in current market conditions, readily available information on nonperformance risk, letters of credit, collateral, other arrangements available, and the nature of master netting arrangements. TVA is a counterparty to currency swaps, interest rate swaps, commodity contracts, and other derivatives which subject TVA to nonperformance risk. Nonperformance risk on the majority of investments and certain exchange-traded instruments held by TVA is incorporated into the exit price that is derived from quoted market data that is used to mark the investment to market. Nonperformance risk for most of TVA's derivative instruments is an adjustment to the initial asset/liability fair value. TVA adjusts for nonperformance risk, both of TVA (for liabilities) and the counterparty (for assets), by applying credit valuation adjustments ("CVAs") . TVA determines an appropriate CVA for each applicable financial instrument based on the term of the instrument and TVA's or the counterparty's credit rating as obtained from Moody's. For companies that do not have an observable credit rating, TVA uses internal analysis to assign a comparable rating to the counterparty. TVA discounts each financial instrument using the historical default rate (as reported by Moody's for CY 1983 to CY 2018) for companies with a similar credit rating over a time period consistent with the remaining term of the contract. The application of CVAs resulted in a less than $1 million decrease in the fair value of both assets and liabilities at December 31, 2019 . Fair Value Measurements The following tables set forth by level, within the fair value hierarchy, TVA's financial assets and liabilities that were measured at fair value on a recurring basis at December 31, 2019 , and September 30, 2019 . Financial assets and liabilities have been classified in their entirety based on the lowest level of input that is significant to the fair value measurement. TVA's assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the determination of the fair value of the assets and liabilities and their classification in the fair value hierarchy levels. Fair Value Measurements Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 509 $ — $ — $ 509 Government debt securities 278 78 — 356 Corporate debt securities — 423 — 423 Mortgage and asset-backed securities — 30 — 30 Institutional mutual funds 266 — — 266 Forward debt securities contracts — 2 — 2 Private credit funds measured at net asset value (1) — — — 52 Private equity funds measured at net asset value (1) — — — 158 Private real asset funds measured at net asset value (1) — — — 142 Commingled funds measured at net asset value (1) — — — 1,225 Total investments 1,053 533 — 3,163 Commodity contract derivatives — 3 1 4 Total $ 1,053 $ 536 $ 1 $ 3,167 Quoted Prices in Active Markets for Identical Liabilities (Level 1) Significant Other Significant Total Liabilities Currency swaps (2) $ — $ 132 $ — $ 132 Interest rate swaps — 1,565 — 1,565 Commodity contract derivatives — 48 18 66 Total $ — $ 1,745 $ 18 $ 1,763 Notes (1) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Consolidated Balance Sheets. (2) TVA records currency swaps net of cash collateral received from or paid to the counterparty, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 14 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . Fair Value Measurements Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 464 $ — $ — $ 464 Government debt securities 279 65 — 344 Corporate debt securities — 417 — 417 Mortgage and asset-backed securities — 32 — 32 Institutional mutual funds 250 — — 250 Forward debt securities contracts — 22 — 22 Private equity funds measured at net asset value (1) — — — 140 Private real estate funds measured at net asset value (1) — — — 135 Private credit measured at net asset value (1) — — — 33 Commingled funds measured at net asset value (1) — — — 1,131 Total investments 993 536 — 2,968 Commodity contract derivatives — 7 5 12 Total $ 993 $ 543 $ 5 $ 2,980 Quoted Prices in Active Markets for Identical Liabilities (Level 1) Significant Other Significant Total Liabilities Currency swaps (2) $ — $ 208 $ — $ 208 Interest rate swaps — 1,764 — 1,764 Commodity contract derivatives — 44 9 53 Total $ — $ 2,016 $ 9 $ 2,025 Notes (1) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Consolidated Balance Sheets. (2) TVA records currency swaps net of cash collateral received from or paid to the counterparty, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 14 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . TVA uses internal valuation specialists for the calculation of its commodity contract derivatives fair value measurements classified as Level 3. Analytical testing is performed on the change in fair value measurements each period to ensure the valuation is reasonable based on changes in general market assumptions. Significant changes to the estimated data used for unobservable inputs, in isolation or combination, may result in significant variations to the fair value measurement reported. The following table presents a reconciliation of all commodity contract derivatives measured at fair value on a recurring basis using significant unobservable inputs (Level 3): Fair Value Measurements Using Significant Unobservable Inputs Commodity Contract Derivatives Three Months Ended Balance at October 1, 2018 $ 58 Change in net unrealized gains (losses) deferred as regulatory assets and liabilities 5 Balance at December 31, 2018 $ 63 Balance at October 1, 2019 $ (4 ) Change in net unrealized gains (losses) deferred as regulatory assets and liabilities (13 ) Balance at December 31, 2019 $ (17 ) The following table presents quantitative information related to the significant unobservable inputs used in the measurement of fair value of TVA's assets and liabilities classified as Level 3 in the fair value hierarchy: Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2019 Valuation Technique(s) Unobservable Inputs Range Assets Commodity contract derivatives $ 1 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $95.63/ton Liabilities Commodity contract derivatives 18 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $95.63/ton Quantitative Information about Level 3 Fair Value Measurements Fair Value at September 30, 2019 Valuation Technique(s) Unobservable Inputs Range Assets Commodity contract derivatives $ 5 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $94.51/ton Liabilities Commodity contract derivatives 9 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $94.51/ton Other Financial Instruments Not Recorded at Fair Value TVA uses the methods and assumptions described below to estimate the fair value of each significant class of financial instrument. The fair value of the financial instruments held at December 31, 2019 , and September 30, 2019 , may not be representative of the actual gains or losses that will be recorded when these instruments mature or are called or presented for early redemption. The estimated values of TVA's financial instruments not recorded at fair value at December 31, 2019 , and September 30, 2019 , were as follows: Estimated Values of Financial Instruments Not Recorded at Fair Value At December 31, 2019 At September 30, 2019 Valuation Classification Carrying Fair Carrying Fair EnergyRight ® receivables (including current portion) Level 2 $ 98 $ 97 $ 101 $ 100 Loans and other long-term receivables, net (including current portion) Level 2 135 124 131 120 EnergyRight ® financing obligation (including current portion) Level 2 110 122 113 126 Unfunded loan commitments Level 2 — 8 — 10 Membership interests of VIEs subject to mandatory redemption (including current portion) Level 2 28 36 28 37 Long-term outstanding power bonds (including current maturities), net Level 2 19,970 25,152 20,124 26,059 Long-term debt of VIEs (including current maturities), net Level 2 1,128 1,360 1,128 1,371 Long-term notes payable (including current maturities) Level 2 22 22 23 23 The carrying value of Cash and cash equivalents, Restricted cash and cash equivalents, and Short-term debt, net approximate their fair values. The fair value for loans and other long-term receivables is estimated by determining the present value of future cash flows using a discount rate equal to lending rates for similar loans made to borrowers with similar credit ratings and for similar remaining maturities, where applicable. The fair value of long-term debt and membership interests of VIEs subject to mandatory redemption is estimated by determining the present value of future cash flows using current market rates for similar obligations, giving effect to credit ratings and remaining maturities.

Other Income (Expense), Net

Other Income (Expense), Net	3 Months Ended
	Dec. 31, 2019
Other Income and Expenses [Abstract]
Other Income (Expense), Net	uring the three months ended December 31, 2019 , Other income (expense), net decreased $12 million as compared to the same period of the prior year primarily driven by $ 21 million of other income in 2018 related to a deposit liability received by TVA as a down payment on the sale of Bellefonte Nuclear Plant ("Bellefonte"). The purchaser, Nuclear Development, LLC, failed to fulfill the requirements of the sales contract with respect to obtaining Nuclear Regulatory Commission ("NRC") approval of the transfer of required nuclear licenses and payment of the remainder of the selling price before the November 30, 2018, closing date. Partially offsetting the income related to the Bellefonte sale was $7 million of unrealized losses in 2018 on the SERP and DCP investments. See Note 19 — Contingencies and Legal Proceedings — Legal Proceedings for a discussion of the lawsuit filed by Nuclear Development, LLC.

Benefit Plans

Benefit Plans	3 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans TVA sponsors a qualified defined benefit plan ("pension plan") that covers most of its full-time employees hired before July 1, 2014, a qualified defined contribution plan ("401(k) plan") that covers most of its full-time employees, two unfunded post-retirement health care plans that provide for non-vested contributions toward the cost of eligible retirees' medical coverage, other post-employment benefits, such as workers' compensation, and the SERP. The pension plan and the 401(k) plan are administered by a separate legal entity, the TVA Retirement System ("TVARS") , which is governed by its own board of directors. The components of net periodic benefit cost and other amounts recognized as changes in regulatory assets for the three months ended December 31, 2019 and 2018 , were as follows: Components of TVA's Benefit Plans (1) For the Three Months Ended Pension Benefits Other Post-Retirement Benefits 2019 2018 2019 2018 Service cost $ 12 $ 12 $ 4 $ 3 Interest cost 104 123 4 4 Expected return on plan assets (122 ) (119 ) — — Amortization of prior service credit (24 ) (25 ) (6 ) (6 ) Recognized net actuarial loss 109 82 2 1 Total net periodic benefit cost as actuarially determined 79 73 4 2 Amount expensed (capitalized) due to actions of regulator (2 ) 3 — — Total net periodic benefit cost $ 77 $ 76 $ 4 $ 2 Note (1) The components of net benefit cost other than the service cost component are included in Other net periodic benefit cost on the Consolidated Statements of Operations. TVA's minimum required pension plan contribution for 2020 is $300 million . TVA contributes $25 million per month to TVARS and as of December 31, 2019 , had contributed $ 75 million . The remaining $ 225 million will be contributed by September 30, 2020. For the three months ended December 31, 2019 , TVA also contributed $ 24 million to the 401(k) plan and $ 10 million (net of $1 million in rebates) to the other post-retirement plans. TVA expects to contribute $ 5 million to the SERP in the second quarter of 2020.

Contingencies and Legal Proceed

Contingencies and Legal Proceedings	3 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Legal Proceedings	Contingencies and Legal Proceedings Contingencies Nuclear Insurance . Section 170 of the Atomic Energy Act, commonly known as the Price-Anderson Act, provides a layered framework of financial protection to compensate for liability claims of members of the public for personal injury and property damages arising from a nuclear incident in the U.S. This financial protection consists of two layers of coverage: • The primary level is private insurance underwritten by American Nuclear Insurers ("ANI") and provides public liability insurance coverage of $450 million for each nuclear power plant licensed to operate. If this amount is not sufficient to cover claims arising from a nuclear incident, the second level, Secondary Financial Protection, applies. • Within the Secondary Financial Protection level, the licensee of each nuclear reactor has a contingent obligation to pay a retrospective premium, equal to its proportionate share of the loss in excess of the primary level, regardless of proximity to the incident of fault, up to a maximum of approximately $138 million per reactor per incident. With TVA's seven reactors, the maximum total contingent obligation per incident is $963 million . This retrospective premium is payable at a maximum rate currently set at approximately $20 million per year per incident per reactor. Currently, 98 reactors are participating in the Secondary Financial Protection program. In the event that a nuclear incident results in public liability claims, the primary level provided by ANI combined with the Secondary Financial Protection should provide up to approximately $14.0 billion in coverage. Federal law requires that each NRC power reactor licensee obtain property insurance from private sources to cover the cost of stabilizing and decontaminating a reactor and its station site after an accident. TVA carries property, decommissioning liability, and decontamination liability insurance from Nuclear Electric Insurance Limited ("NEIL") with limits up to $2.1 billion available for a loss at TVA's three sites. Some of this insurance may require the payment of retrospective premiums up to a maximum of approximately $139 million . TVA purchases accidental outage (business interruption) insurance for TVA's nuclear sites from NEIL. In the event that an accident covered by this policy takes a nuclear unit offline or keeps a nuclear unit offline, NEIL will pay TVA, after a waiting period, an indemnity (a set dollar amount per week) with a maximum indemnity of $ 490 million per unit. This insurance policy may require the payment of retrospective premiums up to a maximum of approximately $ 46 million , but only to the extent the retrospective premium is deemed necessary by the NEIL Board of Directors to pay losses unable to be covered by NEIL's surplus. Decommissioning Costs . TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets related primarily to nuclear generating plants, coal-fired generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. See Note 11 — Asset Retirement Obligations . Nuclear Decommissioning . Provision for decommissioning costs of nuclear generating units is based on options prescribed by the NRC procedures to dismantle and decontaminate the facilities to meet the NRC criteria for license termination. At December 31, 2019 , $3.2 billion , representing the discounted value of future estimated decommissioning costs, was included in AROs. The actual decommissioning costs may vary from the derived estimates because of, among other things, changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. Utilities that own and operate nuclear plants are required to use different procedures in calculating nuclear decommissioning costs under GAAP than those that are used in calculating nuclear decommissioning costs when reporting to the NRC. The two sets of procedures produce different estimates for the costs of decommissioning primarily because of differences in the underlying assumptions. TVA maintains a NDT to provide funding for the ultimate decommissioning of its nuclear power plants. See Note 15 — Fair Value Measurements — Investment Funds . TVA monitors the value of its NDT and believes that, over the long term and before cessation of nuclear plant operations and commencement of decommissioning activities, adequate funds from investments and additional contributions, if necessary, will be available to support decommissioning. TVA's operating nuclear power units are licensed through various dates between 2033-2055, depending on the unit. It may be possible to extend the operating life of some of the units with approval from the NRC. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations . Non-Nuclear Decommissioning . The estimated future non-nuclear decommissioning ARO was $2.6 billion at December 31, 2019 . This decommissioning cost estimate involves estimating the amount and timing of future expenditures and making judgments concerning whether or not such costs are considered a legal obligation. Estimating the amount and timing of future expenditures includes, among other things, making projections of the timing and duration of the asset retirement process and how costs will escalate with inflation. The actual decommissioning costs may vary from the derived estimates because of changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. TVA maintains an ART to help fund the ultimate decommissioning of its non-nuclear power assets. See Note 15 — Fair Value Measurements — Investment Funds . Estimates involved in determining if additional funding will be made to the ART include inflation rate, rate of return projections on the fund investments, and the planned use of other sources to fund decommissioning costs. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations . Environmental Matters. TVA's power generation activities, like those across the utility industry and in other industrial sectors, are subject to federal, state, and local environmental laws and regulations. Major areas of regulation affecting TVA's activities include air quality control, water quality control, and management and disposal of solid and hazardous wastes. In the future, regulations in all of these areas are expected to become more stringent. Regulations are also expected to have a particular emphasis on climate change, renewable generation, and energy efficiency. TVA has incurred, and expects to continue to incur, substantial capital and operating and maintenance costs to comply with evolving environmental requirements primarily associated with, but not limited to, the operation of TVA's coal-fired generating units. Environmental requirements placed on the operation of TVA's coal-fired and other generating units will likely continue to become more restrictive over time. Litigation over emissions or discharges from coal-fired generating units is also occurring. Failure to comply with environmental and safety laws can result in TVA being subject to enforcement actions, which can lead to the imposition of significant civil liability, including fines and penalties, criminal sanctions, and/or the shutting down of non-compliant facilities . TVA estimates that compliance with existing and future Clean Air Act ("CAA") requirements (excluding greenhouse gas ("GHG") requirements) could lead to costs of $ 132 million from 2020 to 2024 , which include existing controls capital projects and air operations and maintenance projects. TVA also estimates additional expenditures of approximately $ 1.1 billion from 2020 to 2024 relating to TVA's CCR conversion program, as well as expenditures of approximately $ 261 million from 2020 to 2024 relating to compliance with Clean Water Act requirements. Future costs could differ from these estimates if new environmental laws or regulations become applicable to TVA or the facilities it operates, or if existing environmental laws or regulations are revised or reinterpreted. There could also be costs that cannot reasonably be predicted at this time, due to uncertainty of actions, that could increase these estimates. Liability for releases and cleanup of hazardous substances is primarily regulated by the federal Comprehensive Environmental Response, Compensation, and Liability Act, and other federal and parallel state statutes. In a manner similar to many other industries and power systems, TVA has generated or used hazardous substances over the years. TVA operations at some facilities have resulted in contamination that TVA is addressing. At December 31, 2019 , and September 30, 2019 , TVA's estimated liability for cleanup and similar environmental work for those sites for which sufficient information is available to develop a cost estimate was approximately $13 million and $15 million , respectively, on a non-discounted basis, and was included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. Potential Liability Associated with Workers' Exposure to CCR Materials. In response to the 2008 ash spill at Kingston, TVA hired Jacobs Engineering Group, Inc. ("Jacobs") to oversee certain aspects of the cleanup. After the cleanup was completed, Jacobs was sued in the United States District Court for the Eastern District of Tennessee ("Eastern District") by employees of a contractor involved in the cleanup and family members of some of the employees. The plaintiffs alleged that Jacobs had failed to take or provide proper health precautions and misled workers about the health risks associated with exposure to coal fly ash, which is a CCR material. The plaintiffs alleged that exposure to the fly ash caused a variety of significant health issues and illnesses, including in some cases death. The case was split into two phases, with the first phase considering, among other issues, general causation and the second determining specific causation and damages. On November 7, 2018, a jury hearing the first phase returned a verdict in favor of the plaintiffs, including determinations that Jacobs failed to adhere to its contract with TVA or the Site Wide Safety and Health Plan in place; Jacobs failed to provide reasonable care to the plaintiffs; and Jacobs's failures were capable of causing a list of medical conditions, ranging from hypertension to cancer. On January 11, 2019, the district court referred the parties to mediation. Depending on the outcome of mediation, the litigation will proceed to the second phase on the question of whether Jacobs's failures did in fact cause the plaintiffs' alleged injuries and damages. Mediation is currently ongoing. On May 13, 2019, an additional group of contractor employees and family members filed suit against Jacobs in the Circuit Court for Roane County, Tennessee. These plaintiffs have raised similar claims to those being litigated in the case referenced above. While TVA is not a party to either of these lawsuits, TVA could be contractually obligated to reimburse Jacobs for some amounts that Jacobs is required to pay. TVA will continue monitoring the litigation to determine whether these or similar cases could have broader implications for the utility industry. Legal Proceedings From time to time, TVA is party to or otherwise involved in lawsuits, claims, proceedings, investigations, and other legal matters ("Legal Proceedings") that have arisen in the ordinary course of conducting TVA's activities, as a result of a catastrophic event or otherwise. General. At December 31, 2019 , TVA had accrued $ 13 million of probable losses with respect to Legal Proceedings, which is included in Other long-term liabilities. No assurance can be given that TVA will not be subject to significant additional claims and liabilities. If actual liabilities significantly exceed the estimates made, TVA's results of operations, liquidity, and financial condition could be materially adversely affected. Environmental Agreements . In April 2011, TVA entered into two substantively similar agreements, one with the Environmental Protection Agency ("EPA") and the other with Alabama, Kentucky, North Carolina, Tennessee, and three environmental advocacy groups: the Sierra Club, the National Parks Conservation Association, and Our Children's Earth Foundation (collectively, the "Environmental Agreements"). They became effective in June 2011. Under the Environmental Agreements, TVA committed to (1) retire on a phased schedule 18 coal-fired units with a combined summer net dependable capability of 2,200 MW, (2) control, convert, or retire additional coal-fired units with a combined summer net dependable capability of 3,500 MW, (3) comply with annual, declining emission caps for sulfur dioxide ("SO 2 ") and nitrogen oxide, (4) invest $ 290 million in certain TVA environmental projects (of which TVA had spent approximately $279 million as of December 31, 2019 ), (5) provide $ 60 million to Alabama, Kentucky, North Carolina, and Tennessee to fund environmental projects, and (6) pay civil penalties of $ 10 million . In exchange for these commitments, most past claims against TVA based on alleged New Source Review and associated violations were waived and cannot be brought against TVA. Future claims, including those for sulfuric acid mist and GHG emissions, can still be brought against TVA, and claims for increases in particulates can also be pursued at many of TVA's coal-fired units. Additionally, the Environmental Agreements do not address compliance with new laws and regulations or the cost associated with such compliance. The liabilities related to the Environmental Agreements are included in Accounts payable and accrued liabilities and Other long-term liabilities on the December 31, 2019 Consolidated Balance Sheets. In conjunction with the approval of the Environmental Agreements, the TVA Board determined that it was appropriate to record TVA's obligations under the Environmental Agreements as regulatory assets, and they are included as such on the December 31, 2019 , Consolidated Balance Sheets and will be recovered in rates in future periods. TVA has substantially completed the requirements in the Environmental Agreements related to retiring coal-fired units or installing controls on such units. Case Involving Kingston Fossil Plant . On May 7, 2019, Roane County and the Cities of Kingston and Harriman ("local governments") filed a lawsuit in the Circuit Court for Roane County, Tennessee, against TVA and Jacobs for monetary damages and unspecified injunctive relief relating to TVA's cleanup response to the 2008 ash spill at Kingston. The local governments allege that TVA and Jacobs failed to take proper measures to mitigate environmental and health risks during the cleanup response and misled the local governments and their citizens about health and environmental risks associated with exposure to coal fly ash. The local governments seek to recover monetary damages on behalf of their citizens for personal injury and property loss claims, damages for lost tax revenue, damages for increased emergency and medical response costs claims, punitive damages, and unspecified injunctive relief. On June 6, 2019, TVA removed the lawsuit to the Eastern District, and TVA and Jacobs filed separate motions to dismiss. Plaintiffs, in response, filed a response opposing both motions and a separate motion seeking leave to file a proposed amended class action complaint in which Roane County would serve as class representative for the municipalities and their citizens. In December 2019, the federal court ruled that the local governments did not have standing to assert representative claims on behalf of their citizens and rejected their motion to proceed as a class action on behalf of their citizens because of the dissimilarity of the injuries allegedly suffered by the local governments (lost tax revenue) and the personal injuries and personal medical expenses allegedly suffered by the individuals. The court indicated, however, that the local governments may have legal standing to assert claims for their direct injuries (claims relating to municipally owned property) and directed the local governments to file an amended pleading in conformance with the court's order by January 16, 2020. The plaintiffs filed their amended complaint on January 15, 2020. Trial is set for April 2021. Class Action Lawsuit Involving Kingston Fossil Plant . On November 7, 2019, a resident of Roane County, Tennessee, filed a proposed class action lawsuit against Jacobs and TVA in the Eastern District. The complaint alleges that the class representative and all other members of the proposed class were damaged as a result of the 2008 ash spill at Kingston and the resulting cleanup activities. The complaint alleges, among other things, that (1) TVA was negligent in its construction and operation of the Kingston CCR facility, (2) TVA and Jacobs failed to take proper measures to mitigate environmental and health risks during the cleanup response, and (3) TVA and Jacobs misled the community about health and environmental risks associated with exposure to coal fly ash. The complaint seeks monetary damages and injunctive relief in the form of an order requiring the defendants to establish a blood testing program and medical monitoring protocol and to remediate damage to the properties of the proposed class. The plaintiff did not attempt to serve TVA with the complaint until January 2020, and TVA will have 60 days from the date service is perfected to respond to the lawsuit. Consent Decree Involving Colbert Fossil Plant. In May 2013, the Alabama Department of Environmental Management ("ADEM") and TVA entered into a consent decree concerning alleged violations of the Alabama Water Pollution Control Act. The consent decree required, among other things, that TVA continue remediation efforts TVA had begun prior to the suit being filed and stop using an unlined landfill after a lined landfill is approved and constructed. In August 2018, the parties agreed to amend the consent decree to deal with groundwater issues identified after TVA published groundwater monitoring reports in accordance with the EPA's CCR rule (the "CCR Rule"). The amended consent decree requires TVA to investigate the nature and extent of any groundwater contamination, develop and implement a remedy, provide semiannual status reports to ADEM, and remedy any seeps identified during inspections. TVA also paid $100,000 to Alabama under the amended consent decree. In accordance with the amended consent decree, TVA submitted to ADEM a Comprehensive Groundwater Investigation Report on May 17, 2019, and an Assessment of Corrective Measures on July 17, 2019. TVA is continuing to develop the groundwater remedy and submit reports to ADEM. Case Involving Tennessee River Boat Accident . On July 23, 2015, plaintiffs filed suit in the United States District Court for the Northern District of Alabama ("Northern District"), seeking recovery for personal injuries sustained when the plaintiffs' boat struck a TVA transmission line which was being raised from the Tennessee River during a repair operation. The district court dismissed the case, finding that TVA's exercise of its discretion as a governmental entity in deciding how to carry out the operation barred any liability for negligence. In August 2017, the U.S. Court of Appeals for the Eleventh Circuit ("Eleventh Circuit") affirmed the decision. The plaintiffs petitioned the U.S. Supreme Court ("Supreme Court") for review of the decision, arguing that the provision of the TVA Act which allows suit to be brought against TVA does not allow TVA to claim immunity for discretionary actions. On April 29, 2019, the Supreme Court issued its opinion reversing the judgment of the Eleventh Circuit and remanding the case to the Eleventh Circuit. On July 17, 2019, the Eleventh Circuit remanded the case to the district court for further proceedings consistent with the Supreme Court's opinion. Trial is currently scheduled for February 16, 2021. Case Involving Bellefonte Nuclear Plant. On November 30, 2018, Nuclear Development, LLC, filed suit against TVA in the Northern District. The plaintiff alleges that TVA breached its agreement to sell Bellefonte to the plaintiff. The plaintiff seeks, among other things, (1) an injunction requiring TVA to maintain Bellefonte and the associated NRC permits until the case is concluded, (2) an order compelling TVA to complete the sale of Bellefonte to the plaintiff, and (3) if the court does not order TVA to complete the sale, monetary damages in excess of $ 30 million . On December 26, 2018, Nuclear Development, LLC, and TVA filed a joint stipulation with the court. Under the stipulation, Nuclear Development, LLC, withdrew its request for an expedited hearing on its injunction in exchange for TVA's agreement to continue to maintain Bellefonte in accordance with the NRC permits and to give Nuclear Development, LLC, and the court five days prior notice of any filing by TVA to terminate the permits or sell the site. TVA filed a motion to dismiss the case on February 4, 2019. On May 15, 2019, the court denied TVA's motion. The case is scheduled to be ready for trial by July 2020.

Revenue (Notes)

Revenue (Notes)	3 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue Revenue from Sales of Electricity TVA's revenue from contracts with customers is primarily derived from the generation and sale of electricity to its customers and is included in Revenue from sales of electricity on the Consolidated Statements of Operations. Electricity is sold primarily to LPCs for distribution to their end-use customers. In addition, TVA sells electricity to directly served industrial companies, federal agencies, and others. LPC sales Approximately 93 percent of TVA's revenue from sales of electricity is to LPCs, which then distribute the power to their customers using their own distribution systems. Power is delivered to each LPC at delivery points within the LPC's service territory. TVA recognizes revenue when the customer takes possession of the power at the delivery point. For power sales, the performance obligation to deliver power is satisfied in a series over time because the sales of electricity over the term of the customer contract are a series of distinct goods that are substantially the same and have the same pattern of transfer to the customer. TVA has no continuing performance obligations subsequent to delivery. Using the output method for revenue recognition provides a faithful depiction of the transfer of electricity as customers obtain control of the power and benefit from its use at delivery. Additionally, TVA has an enforceable right to consideration for energy delivered at any discrete point in time and will recognize revenue at an amount that reflects the consideration to which TVA is entitled for the energy delivered. Directly served customers Directly served customers, including industrial customers, federal agencies, and other customers, take power for their own consumption. Similar to LPCs, power is delivered to a delivery point, at which time the customer takes possession and TVA recognizes revenue. For all power sales, the performance obligation to deliver power is satisfied in a series over time since the sales of electricity over the term of the customer contract are a series of distinct goods that are substantially the same and have the same pattern of transfer to the customer. TVA has no continuing performance obligations subsequent to delivery. Using the output method for revenue recognition provides a faithful depiction of the transfer of electricity as customers obtain control of the power and benefit from its use at delivery. Additionally, TVA has an enforceable right to consideration for energy delivered at any discrete point in time and will recognize revenue at an amount that reflects the consideration to which TVA is entitled for the energy delivered. The amount of revenue is based on contractual prices approved by the TVA Board. Customers are invoiced monthly for power delivered as measured by meters located at the delivery points. The net transaction price is offset by certain credits available to customers that are known at the time of billing. Examples of credits include items such as economic development credits to promote growth in the Tennessee Valley and interruptible credits allowing TVA to reduce industrial customer usage in periods of peak demand to balance system demand. Payments are typically due within approximately one month of invoice issuance. Other Revenue Other revenue consists primarily of wheeling and network transmission charges, sales of excess steam that is a by-product of power production, delivery point charges for interconnection points between TVA and the customer, and certain other ancillary goods or services. Disaggregated Revenue During the three months ended December 31, 2019 , revenues generated from TVA's electricity sales were $2.5 billion and accounted for virtually all of TVA's revenues. TVA's revenues by state for the three months ended December 31, 2019 and 2018 are detailed in the table below: Operating Revenues By State Three Months Ended December 31 (in millions) 2019 2018 Alabama $ 369 $ 392 Georgia 63 67 Kentucky 157 168 Mississippi 237 251 North Carolina 18 20 Tennessee 1,676 1,771 Virginia 11 12 Subtotal 2,531 2,681 Off-system sales 1 — Revenue from sales of electricity 2,532 2,681 Other revenue 46 44 Total operating revenues $ 2,578 $ 2,725 TVA's revenues by customer type for the three months ended December 31, 2019 and 2018 are detailed in the table below: Operating Revenues by Customer Type Three Months Ended December 31 (in millions) 2019 2018 Revenue from sales of electricity Local power companies (1) $ 2,357 $ 2,468 Industries directly served 150 184 Federal agencies and other 25 29 Revenue from sales of electricity 2,532 2,681 Other revenues 46 44 Total operating revenues $ 2,578 $ 2,725 Note (1) The amount for the three months ended December 31, 2019, is net of $34 million of wholesale bill credits to LPCs participating in the long-term Partnership Agreement. TVA and LPCs continue to work together to meet the changing needs of consumers around the Tennessee Valley. At its August 2019 meeting, the TVA Board approved a 20-year Partnership Agreement option that better aligns the length of LPC contracts with TVA's long-term commitments. These agreements are automatically extended each year after their initial effective date, contingent upon certain circumstances, including agreement on flexibility options and limited rate increases going forward. Participating LPCs will receive benefits including a 3.1 percent wholesale bill credit in exchange for their long-term commitment, which enables TVA to recover its long-term financial commitments over a commensurate period. In addition, participating LPCs will have the option for flexible generation capacity up to approximately five percent of average total hourly energy sales over the prior five years. As of December 31, 2019 , 134 LPCs had signed the 20-year Partnership Agreement with TVA. The number of LPCs with the contract arrangements described below, the revenues derived from such arrangements for the three months ended December 31, 2019 , and the percentage of TVA's total operating revenues for the three months ended December 31, 2019 represented by these revenues are summarized in the tables below: TVA Local Power Company Contracts Contract Arrangements (1) Number of LPCs Revenue from Sales of Electricity to LPCs Percentage of Total Operating Revenues 20-year termination notice 134 $ 1,471 57.1 % 10-year termination notice 4 214 8.3 5-year termination notice 16 672 26.1 Total 154 $ 2,357 91.5 % Note (1) Ordinarily, the LPCs and TVA have the same termination notice period; however, in contracts with three of the LPCs with five-year termination notices, TVA has a 10-year termination notice (which becomes a five-year termination notice if TVA loses its discretionary wholesale rate-setting authority). Certain LPCs have five-year termination notices or a shorter period if any act of Congress, court decision, or regulatory change requires or permits that election. TVA's two largest LPCs — Memphis Light, Gas and Water Division ("MLGW") and Nashville Electric Service ("NES") — have contracts with a five-year and a 20-year termination notice period, respectively. Sales to MLGW and NES each accounted for eight percent of TVA's total operating revenues during the three months ended December 31, 2019 and 2018. Contract Balances Contract assets represent an entity's right to consideration in exchange for goods and services that the entity has transferred to customers. TVA does not have any material contract assets at December 31, 2019 . Contract liabilities represent an entity's obligations to transfer goods or services to customers for which the entity has received consideration (or an amount of consideration is due) from the customers. These contract liabilities are primarily related to upfront consideration received prior to the satisfaction of the performance obligation. Economic Development Incentives. Under certain economic development programs, TVA offers incentives to existing and potential power customers in certain business sectors that make multi-year commitments to invest in the Tennessee Valley. TVA records those incentives as reductions of revenue. Incentives recorded as a reduction to revenue were $ 76 million and $ 67 million during the three months ended December 31, 2019 , and 2018 , respectively. Incentives that have been approved but have not been paid are recorded in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. At December 31, 2019 and September 30, 2019 , the outstanding unpaid incentives were $ 158 million and $ 157 million , respectively. These incentives may be subject to clawback provisions if the customers fail to meet certain program requirements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue Recognition [Line Items]
Reclassification of Amounts on Cash Flow and Statement of Operations [Table Text Block]		Reclassifications Certain historical amounts have been reclassified in the accompanying consolidated financial statements to the current presentation. In the December 31, 2018, Consolidated Statements of Cash Flows, amounts previously reported as $(10) million of Accounts payable and accrued liabilities were reclassified to Other, net in cash flows from operating activities. Additionally, amounts previously reported as $(10) million of Prepayment credits applied to revenue were reclassified to Other, net in cash flows from operating activities.
General	General The Tennessee Valley Authority ("TVA") is a corporate agency and instrumentality of the United States ("U.S.") that was created in 1933 by federal legislation in response to a proposal by President Franklin D. Roosevelt. TVA was created to, among other things, improve navigation on the Tennessee River, reduce the damage from destructive flood waters within the Tennessee River system and downstream on the lower Ohio and Mississippi Rivers, further the economic development of TVA's service area in the southeastern U.S., and sell the electricity generated at the facilities TVA operates. Today, TVA operates the nation's largest public power system and supplies power in most of Tennessee, northern Alabama, northeastern Mississippi, and southwestern Kentucky and in portions of northern Georgia, western North Carolina, and southwestern Virginia to a population of nearly 10 million people. TVA also manages the Tennessee River, its tributaries, and certain shorelines to provide, among other things, year-round navigation, flood damage reduction, and affordable and reliable electricity. Consistent with these primary purposes, TVA also manages the river system and public lands to provide recreational opportunities, adequate water supply, improved water quality, cultural and natural resource protection, and economic development. The power program has historically been separate and distinct from the stewardship programs. It is required to be self-supporting from power revenues and proceeds from power financings, such as proceeds from the issuance of bonds, notes, or other evidences of indebtedness (collectively, "Bonds") . Although TVA does not currently receive congressional appropriations, it is required to make annual payments to the U.S. Department of the Treasury ("U.S. Treasury") as a return on the government's appropriation investment in TVA's power facilities (the "Power Program Appropriation Investment"). In the 1998 Energy and Water Development Appropriations Act, Congress directed TVA to fund essential stewardship activities related to its management of the Tennessee River system and nonpower or stewardship properties with power revenues in the event that there were insufficient appropriations or other available funds to pay for such activities in any fiscal year. Congress has not provided any appropriations to TVA to fund such activities since 1999. Consequently, during 2000, TVA began paying for essential stewardship activities primarily with power revenues, with the remainder funded with user fees and other forms of revenues derived in connection with those activities. The activities related to stewardship properties do not meet the criteria of an operating segment under accounting principles generally accepted in the United States of America ("GAAP") . Accordingly, these assets and properties are included as part of the power program, TVA's only operating segment. Power rates are established by the TVA Board of Directors (the "TVA Board") as authorized by the Tennessee Valley Authority Act of 1933, as amended (the "TVA Act"). The TVA Act requires TVA to charge rates for power that will produce gross revenues sufficient to provide funds for operation, maintenance, and administration of its power system; payments to states and counties in lieu of taxes ("tax equivalents") ; debt service on outstanding indebtedness; payments to the U.S. Treasury in repayment of and as a return on the Power Program Appropriation Investment; and such additional margin as the TVA Board may consider desirable for investment in system assets, retirement of outstanding Bonds in advance of maturity, additional reduction of the Power Program Appropriation Investment, and other purposes connected with TVA's business. TVA fulfilled its requirement to repay $1.0 billion of the Power Program Appropriation Investment with the 2014 payment; therefore, this item is no longer a component of rate setting. In setting TVA's rates, the TVA Board is charged by the TVA Act to have due regard for the primary objectives of the TVA Act, including the objective that power shall be sold at rates as low as are feasible. Rates set by the TVA Board are not subject to review or approval by any state or federal regulatory body.
Fiscal Year	Fiscal Year TVA's fiscal year ends September 30. Years ( 2020 , 2019 , etc.) refer to TVA's fiscal years unless they are preceded by "CY," in which case the references are to calendar years.
Cost-Based Regulation	Cost-Based Regulation Since the TVA Board is authorized by the TVA Act to set rates for power sold to its customers, TVA is self-regulated. Additionally, TVA's regulated rates are designed to recover its costs. Based on current projections, TVA believes that rates, set at levels that will recover TVA's costs, can be charged and collected. As a result of these factors, TVA records certain assets and liabilities that result from the regulated ratemaking process that would not be recorded under GAAP for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred because such costs are probable of future recovery in customer rates. Regulatory liabilities generally represent obligations to make refunds to customers for previous collections for costs that are not likely to be incurred or deferral of gains that will be credited to customers in future periods. TVA assesses whether the regulatory assets are probable of future recovery by considering factors such as applicable regulatory changes, potential legislation, and changes in technology. Based on these assessments, TVA believes the existing regulatory assets are probable of recovery. This determination reflects the current regulatory and political environment and is subject to change in the future. If future recovery of regulatory assets ceases to be probable, or any of the other factors described above cease to be applicable, TVA would no longer be considered to be a regulated entity and would be required to write off these costs. All regulatory asset write-offs would be required to be recognized in earnings in the period in which future recovery ceases to be probable.
Basis of Presentation	Basis of Presentation TVA prepares its consolidated interim financial statements in conformity with GAAP for consolidated interim financial information. Accordingly, TVA's consolidated interim financial statements do not include all of the information and notes required by GAAP for annual financial statements. As such, they should be read in conjunction with the audited financial statements for the year ended September 30, 2019 , and the notes thereto, which are contained in TVA's Annual Report on Form 10-K/A for the year ended September 30, 2019 (the "Annual Report"). In the opinion of management, all adjustments (consisting of items of a normal recurring nature) considered necessary for fair presentation are included on the consolidated interim financial statements. The accompanying consolidated interim financial statements, which have been prepared in accordance with GAAP, include the accounts of TVA, wholly-owned direct subsidiaries, and variable interest entities ("VIE") of which TVA is the primary beneficiary. See Note 9 — Variable Interest Entities . Intercompany balances and transactions have been eliminated in consolidation
Use of Estimates	Use of Estimates The preparation of financial statements requires TVA to estimate the effects of various matters that are inherently uncertain as of the date of the consolidated financial statements. Although the consolidated financial statements are prepared in conformity with GAAP, TVA is required to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the amounts of revenues and expenses reported during the reporting period. Each of these estimates varies in regard to the level of judgment involved and its potential impact on TVA's financial results. Estimates are considered critical either when a different estimate could have reasonably been used, or where changes in the estimate are reasonably likely to occur from period to period, and such use or change would materially impact TVA's financial condition, results of operations, or cash flows.
Restricted cash	Cash, Cash Equivalents, and Restricted Cash Cash includes cash on hand, non-interest bearing cash, and deposit accounts. All highly liquid investments with original maturities of three months or less are considered cash equivalents. Cash and cash equivalents that are restricted, as to withdrawal or use under the terms of certain contractual agreements, are recorded in Other long-term assets on the Consolidated Balance Sheets. Restricted cash and cash equivalents includes cash held in trusts that are currently restricted for TVA economic development loans and for certain TVA environmental programs in accordance with agreements related to compliance with certain environmental regulations. See Note 19 — Contingencies and Legal Proceedings — Legal Proceedings — Environmental Agreements . The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported on the Consolidated Balance Sheets and Consolidated Statements of Cash Flows: Cash, Cash Equivalents, and Restricted Cash At December 31, 2019 At September 30, 2019 Cash and cash equivalents $ 304 $ 299 Restricted cash and cash equivalents included in Other long-term assets 23 23 Total cash, cash equivalents, and restricted cash $ 327 $ 322	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported on the Consolidated Balance Sheets and Consolidated Statements of Cash Flows: Cash, Cash Equivalents, and Restricted Cash At December 31, 2019 At September 30, 2019 Cash and cash equivalents $ 304 $ 299 Restricted cash and cash equivalents included in Other long-term assets 23 23 Total cash, cash equivalents, and restricted cash $ 327 $ 322
Revenue Recognition [Table Text Block]		Revenues TVA recognizes revenue from contracts with customers to depict the transfer of goods or services to customers in an amount to which the entity expects to be entitled in exchange for those goods or services. For the generation and transmission of electricity, this is generally at the time the power is delivered to a metered customer delivery point for the customer's consumption or distribution. As a result, revenues from power sales are recorded as electricity is delivered to customers. In addition to power sales invoiced and recorded during the month, TVA accrues estimated unbilled revenues for power sales provided to five customers whose billing date occurs prior to the end of the month. Exchange power sales are presented in the accompanying Consolidated Statements of Operations as a component of sales of electricity. Exchange power sales are sales of excess power after meeting TVA native load and directly served requirements. Native load refers to the customers on whose behalf a company, by statute, franchise, regulatory requirement, or contract, has undertaken an obligation to serve. TVA engages in other arrangements in addition to power sales. Certain other revenue from activities related to TVA's overall mission are recorded in Other revenue. Revenues that are not related to the overall mission are recorded in Other income (expense), net.
Allowance for Uncollectible Accounts	Allowance for Uncollectible Accounts The allowance for uncollectible accounts reflects TVA's estimate of probable losses inherent in its accounts and loans receivable balances, excluding the EnergyRight ® loans receivable. TVA determines the allowance based on known accounts, historical experience, and other currently available information including events such as customer bankruptcy and/or a customer failing to fulfill payment arrangements after 90 days. It also reflects TVA's corporate credit department's assessment of the financial condition of customers and the credit quality of the receivables. The allowance for uncollectible accounts was less than $ 1 million at both December 31, 2019 , and September 30, 2019 , for accounts receivable. Additionally, loans receivable of $135 million and $ 131 million at December 31, 2019 , and September 30, 2019 , respectively, are included in Accounts receivable, net and Other long-term assets, for the current and long-term portions, respectively, and are reported net of allowances for uncollectible accounts of less than $ 1 million at both December 31, 2019 , and September 30, 2019 .
Depreciation	Depreciation TVA accounts for depreciation of its properties using the composite depreciation convention of accounting. Under the composite method, assets with similar economic characteristics are grouped and depreciated as one asset. Depreciation is generally computed on a straight-line basis over the estimated service lives of the various classes of assets. The estimation of asset useful lives requires management judgment, supported by external depreciation studies of historical asset retirement experience. Depreciation rates are determined based on the external depreciation studies. These studies are updated at least every five years. Depreciation expense was $539 million and $308 million for the three months ended December 31, 2019 and 2018 , respectively. See Note 5 — Plant Closures for a discussion of the impact of plant closures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies Leases (Policies)	3 Months Ended
	Dec. 31, 2019
Lease Disclosure [Line Items]
Lease Disclosure [Table Text Block]	Leases TVA recognizes a lease asset and lease liability for leases with terms of greater than 12 months. Lease assets represent TVA's right to use an underlying asset for the lease term, and lease liabilities represent TVA's obligation to make lease payments arising from the lease, both of which are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. TVA has certain lease agreements that include variable lease payments that are based on energy production levels. These variable lease payments are not included in the measurement of the lease assets or lease liabilities but are recognized in the period in which the expenses are incurred. While not specifically structured as leases, certain power purchase agreements are deemed to contain a lease of the underlying generating units when the terms convey the right to control the use of the assets. Amounts recorded for these leases are generally based on the amount of the scheduled capacity payments due over the remaining terms of the purchased power agreements, the terms of which are approximately four years. The total lease obligation included in Operating lease liabilities related to these agreements is $ 130 million at December 31, 2019. TVA has agreements with lease and non-lease components and has elected to account for the components separately. Consideration is allocated to lease and non-lease components generally based on relative standalone selling prices. TVA has lease agreements which include options for renewal and early termination. The intent to renew a lease varies depending on the lease type and asset. Renewal options that are reasonably certain to be exercised are included in the lease measurements. The decision to terminate a lease early is dependent on various economic factors. No termination options have been included in TVA's lease measurements. Leases with an initial term of 12 months or less, which do not include an option to extend the initial term of the lease to greater than 12 months that TVA is reasonably certain to exercise, are not recorded on the Consolidated Balance Sheets at December 31, 2019 . Operating leases are recognized on a straight line basis over the term of the lease agreement. Rent expense associated with short-term leases and variable leases is recorded in Operating and maintenance expense, Fuel expense, or Purchased power expense on the Consolidated Statements of Operations. Expenses associated with finance leases result in the separate presentation of interest expense on the lease liability and amortization expense of the related lease asset on the Consolidated Statements of Operations.

Variable Interest Entities (Pol

Variable Interest Entities (Policies)	3 Months Ended
	Dec. 31, 2019
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity Policy	A VIE is an entity that either (i) has insufficient equity to permit the entity to finance its activities without additional subordinated financial support or (ii) has equity investors who lack the characteristics of owning a controlling financial interest. When TVA determines that it has a variable interest in a VIE, a qualitative evaluation is performed to assess which interest holders have the power to direct the activities that most significantly impact the economic performance of the entity and have the obligation to absorb losses or receive benefits that could be significant to the entity. The evaluation considers the purpose and design of the business, the risks that the business was designed to create and pass along to other entities, the activities of the business that can be directed and which party can direct them, and the expected relative impact of those activities on the economic performance of the business through its life. TVA has the power to direct the activities of an entity when it has the ability to make key operating and financing decisions, including, but not limited to, capital investment and the issuance of debt. Based on the evaluation of these criteria, TVA has determined it is the primary beneficiary of certain entities and as such is required to account for the VIEs on a consolidated basis.

Impact of New Accounting Stan_2

Impact of New Accounting Standards and Interpretations Impact of New Accounting Standards and Interpretations (Tables)	3 Months Ended
	Dec. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	Impact of New Accounting Standards and Interpretations The following are accounting standard updates issued by the Financial Accounting Standards Board ("FASB") that TVA adopted during 2020: Lease Accounting Description This guidance changes the provisions of recognition in both the lessee and lessor accounting models. The standard requires entities that lease assets ("lessees") to recognize on the balance sheet the assets and liabilities for the rights and obligations created by leases with terms of more than 12 months, while also refining the definition of a lease. In addition, lessees are required to disclose key information about the amount, timing, and uncertainty of cash flows arising from leasing arrangements. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily depend on its classification as a finance lease (formerly referred to as capital lease) or operating lease. The standard requires both types of leases to be recognized on the balance sheet. Operating leases will result in straight-line expense, while finance leases will result in recognition of interest on the lease liability separate from amortization expense. The accounting rules for the owner of assets leased by the lessee ("lessor accounting") remain relatively unchanged. The standard allows for certain practical expedients to be elected related to lease term determination, separation of lease and non-lease elements, reassessment of existing leases, and short-term leases. The standard is to be applied using a modified retrospective transition. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters TVA has elected the modified retrospective method of adoption effective October 1, 2019. Under the modified retrospective method of adoption, prior year reported results are not restated. TVA recorded $205 million and $210 million of lease assets and lease liabilities, respectively, for operating leases in effect at the adoption date. The accounting for finance leases remained substantially unchanged. Adoption of the standard did not materially impact results of operations or cash flows. TVA has elected to apply the following practical expedients: Practical Expedient Description Package of transition practical expedients (for leases commenced prior to adoption date; expedients must be adopted as a package) Do not need to (1) reassess whether any expired or existing contracts are leases or contain leases, (2) reassess the lease classification for any expired or existing leases, or (3) reassess initial direct costs for any existing leases. Short-term lease expedient (elect by class of underlying asset) Elect as an accounting policy to not apply the recognition requirements to short-term leases by asset class. Existing and expired land easements not previously accounted for as leases Elect to not evaluate existing or expired easements under the new guidance and carry forward current accounting treatment. Comparative reporting requirements for initial adoption Elect to apply transition requirements at adoption date, recognize cumulative effect adjustment to retained earnings in period of adoption, and not apply the new requirements to comparative periods, including disclosures. Derivatives and Hedging - Improvements to Accounting for Hedging Activities Description This guidance better aligns an entity's risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. To meet that objective, the amendments expand and refine hedge accounting for both nonfinancial and financial risk components and align the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters TVA has adopted the standard on a prospective basis. The adoption of this standard did not have a material impact on TVA's financial condition, results of operations, or cash flows. TVA only uses hedge accounting under its foreign currency swap arrangements, and the adoption of this standard has no impact on those arrangements. Customer's Accounting for Implementation Costs in a Cloud Arrangement That Is a Service Contract Description This guidance relates to the accounting for a customer's implementation costs in a hosting arrangement that is a service contract. The amendments align the requirements for capitalizing those implementation costs with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software and hosting arrangements that include an internal-use software license. The amendments also provide requirements for the classification of the capitalized costs and related expense and cash flows in the financial statements, the application of impairment guidance to the capitalized costs, and the application of abandonment guidance to the capitalized costs. Entities are required to apply the amendments either retrospectively or prospectively to all implementation costs incurred after the adoption date. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters Adoption of this standard did not have a material impact on TVA's financial condition, results of operation, or cash flows. TVA records qualified implementation costs in a cloud arrangement that is a service contract as a prepaid asset and amortizes the prepaid asset to Operating and maintenance expense based on the term of the contract. The following accounting standards have been issued but at December 31, 2019 , were not effective and had not been adopted by TVA: Financial Instruments - Credit Losses Description This guidance eliminates the probable initial recognition threshold in current GAAP and, instead, requires an allowance to be recorded for all expected credit losses for certain financial assets that are not measured at fair value. The allowance for credit losses is based on historical information, current conditions, and reasonable and supportable forecasts. The new standard also makes revisions to the other than temporary impairment model for available-for-sale debt securities. Disclosures of credit quality indicators in relation to the amortized cost of financing receivables are further disaggregated by year of origination. Effective Date for TVA The new standard is effective for TVA's interim and annual reporting periods beginning October 1, 2020. While early adoption is permitted, TVA does not plan to adopt the standard early. Effect on the Financial Statements or Other Significant Matters TVA is working to develop a model to calculate the allowance for credit losses based on management's estimate of the losses expected to be incurred over the life of the asset. TVA is evaluating the potential impact of the changes on its consolidated financial statements and related disclosures. Fair Value Measurement Disclosure Description The guidance changes certain disclosure requirements for fair value measurements. It removes certain disclosure requirements, such as the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; the policy for timing of the transfers between levels; and the valuation processes for Level 3 fair value measurements. Some disclosure requirements are added, such as the change in unrealized gains and losses included in other comprehensive income for recurring Level 3 fair value measurements and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Effective Date for TVA The new standard is effective for TVA's interim and annual reporting periods beginning October 1, 2020. While early adoption is permitted, TVA does not plan to adopt the standard early. Effect on the Financial Statements or Other Significant Matters TVA does not expect the adoption of this standard to have a material impact on TVA's financial condition, results of operations, or cash flows. TVA is evaluating the potential impact on related disclosures.

Accounts Receivable, Net (Table

Accounts Receivable, Net (Tables)	3 Months Ended
	Dec. 31, 2019
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Accounts Receivable, Net	The table below summarizes the types and amounts of TVA's accounts receivable: Accounts Receivable, Net At December 31, 2019 At September 30, 2019 Power receivables $ 1,326 $ 1,624 Other receivables 101 115 Accounts receivable, net (1) $ 1,427 $ 1,739 Note (1) Allowance for uncollectible accounts was less than $ 1 million at December 31, 2019 and September 30, 2019 , and therefore is not represented in the table above.

Inventories, Net (Tables)

Inventories, Net (Tables)	3 Months Ended
	Dec. 31, 2019
Inventory, Net [Abstract]
Inventories, Net	The table below summarizes the types and amounts of TVA's inventories: Inventories, Net At December 31, 2019 At September 30, 2019 Materials and supplies inventory $ 752 $ 742 Fuel inventory 337 294 Renewable energy certificates/emission allowance inventory, net 17 16 Allowance for inventory obsolescence (54 ) (53 ) Inventories, net $ 1,052 $ 999

Other Long-Term Assets (Tables)

Other Long-Term Assets (Tables)	3 Months Ended
	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Long-Term Assets	The table below summarizes the types and amounts of TVA's other long-term assets: Other Long-Term Assets At December 31, 2019 At September 30, 2019 Loans and other long-term receivables, net $ 129 $ 125 EnergyRight ® receivables 78 81 Prepaid long-term service agreements (1) 29 22 Restricted cash and cash equivalents 23 23 Prepaid capacity payments 17 19 Other 58 55 Total other long-term assets $ 334 $ 325

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	3 Months Ended
	Dec. 31, 2019
Revenue from External Customer [Line Items]
Revenue from External Customers by Products and Services [Table Text Block]	TVA's revenues by customer type for the three months ended December 31, 2019 and 2018 are detailed in the table below: Operating Revenues by Customer Type Three Months Ended December 31 (in millions) 2019 2018 Revenue from sales of electricity Local power companies (1) $ 2,357 $ 2,468 Industries directly served 150 184 Federal agencies and other 25 29 Revenue from sales of electricity 2,532 2,681 Other revenues 46 44 Total operating revenues $ 2,578 $ 2,725
Regulatory Assets and Liabilities	Components of regulatory assets and regulatory liabilities are summarized in the table below: Regulatory Assets and Liabilities (1) At December 31, 2019 At September 30, 2019 Current regulatory assets Unrealized losses on interest rate derivatives $ 89 $ 89 Unrealized losses on commodity derivatives 49 39 Fuel cost adjustment receivable 21 28 Total current regulatory assets 159 156 Non-current regulatory assets Deferred pension costs and other post-retirement benefits costs 4,678 4,756 Non-nuclear decommissioning costs 1,725 1,741 Nuclear decommissioning costs 765 868 Unrealized losses on interest rate derivatives 1,074 1,241 Unrealized losses on commodity contracts 17 15 Other non-current regulatory assets 151 142 Total non-current regulatory assets 8,410 8,763 Total regulatory assets $ 8,569 $ 8,919 Current regulatory liabilities Fuel cost adjustment tax equivalents $ 134 $ 138 Unrealized gains on commodity derivatives 3 12 Total current regulatory liabilities $ 137 $ 150

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
	Dec. 31, 2019
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Summary of Impact of VIEs on Consolidated Balance Sheets	The financial statement items attributable to carrying amounts and classifications of JSCCG, Holdco, and SCCG at December 31, 2019 , and September 30, 2019 , as reflected on the Consolidated Balance Sheets, are as follows: Summary of Impact of VIEs on Consolidated Balance Sheets At December 31, 2019 At September 30, 2019 Current liabilities Accrued interest $ 24 $ 11 Accounts payable and accrued liabilities 3 3 Current maturities of long-term debt of variable interest entities 39 39 Total current liabilities 66 53 Other liabilities Other long-term liabilities 25 25 Long-term debt, net Long-term debt of variable interest entities, net 1,089 1,089 Total liabilities $ 1,180 $ 1,167

Other Long-Term Liabilities (Ta

Other Long-Term Liabilities (Tables)	3 Months Ended
	Dec. 31, 2019
Other Liabilities, Noncurrent [Abstract]
Other Long-Term Liabilities	The table below summarizes the types and amounts of Other long-term liabilities: Other Long-Term Liabilities At December 31, 2019 At September 30, 2019 Interest rate swap liabilities $ 1,477 $ 1,676 Finance lease liabilities 180 182 Currency swap liabilities 120 193 EnergyRight ® financing obligation 88 90 Paradise pipeline financing obligation 79 80 Accrued long-term service agreement 61 66 Other 196 203 Total other long-term liabilities $ 2,201 $ 2,490

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation Activity	Asset Retirement Obligation Activity (1) Nuclear Non-Nuclear Total Balance at September 30, 2019 $ 3,136 $ 2,480 $ 5,616 Settlements — (32 ) (32 ) Revisions in estimate — 117 117 Accretion (recorded as regulatory asset) 35 15 50 Balance at December 31, 2019 $ 3,171 $ 2,580 $ 5,751 Note (1) The current portion of ARO in the amount of $163 million at both December 31, 2019 , and September 30, 2019 , is included in Accounts payable and accrued liabilities. The revisions in non-nuclear estimates increased $ 117 million for the three months ended December 31, 2019 . In November 2019, the Tennessee Department of Environment and Conservation ("TDEC") released amendments to its regulations which govern solid waste disposal facilities, including TVA's active Coal Combustion Residuals ("CCR") facilities covered by a solid waste disposal permit and those which closed pursuant to a TDEC approved closure plan. Such facilities are generally subject to a 30-year post-closure care period during which the owner or operator must undertake certain activities, including monitoring and maintaining the facility. The amendments will, among other things, add an additional 50-year period after the end of the post-closure care period, require TVA to submit recommendations as to what activities must be performed during this 50-year period to protect human health and the environment, and require TVA to submit revised closure plans every 10 years. This regulatory revision resulted in an increase of $129 million , of which $38 million was related to operating CCR facilities and $91 million was related to inactive or closed CCR facilities.

Debt and Other Obligations (Tab

Debt and Other Obligations (Tables)	3 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt Outstanding	Total debt outstanding at December 31, 2019 , and September 30, 2019 , consisted of the following: Debt Outstanding At December 31, 2019 At September 30, 2019 Short-term debt Short-term debt, net $ 895 $ 922 Current maturities of power bonds issued at par 1,029 1,030 Current maturities of long-term debt of VIEs issued at par 39 39 Current maturities of notes payable 22 23 Total current debt outstanding, net 1,985 2,014 Long-term debt Long-term power bonds (1) 19,065 19,225 Long-term debt of variable interest entities, net 1,089 1,089 Unamortized discounts, premiums, issue costs, and other (124 ) (131 ) Total long-term debt, net 20,030 20,183 Total outstanding debt $ 22,015 $ 22,197 Note (1) Includes net exchange gain from currency transactions of $133 million and $191 million at December 31, 2019 , and September 30, 2019 , respec
Debt Securities Activity	The table below summarizes the long-term debt securities activity for the period from October 1, 2019, to December 31, 2019 : Debt Securities Activity (1) Date Amount (2) Interest Rate Redemptions/Maturities electronotes ® First Quarter 2020 $ 217 3.33 % 2009 Series B December 2019 1 3.77 % Total redemptions/maturities of debt $ 218 Note (1) Amounts for notes payable were less than $1 million at December 31, 2019, and are therefore not represented in the table above. (2) All redemptions were at 100 percent of par.

Risk Management Activities an_2

Risk Management Activities and Derivative Transactions (Tables)	3 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Derivative Instruments That Receive Hedge Accounting Treatment	The following tables summarize the accounting treatment that certain of TVA's financial derivative transactions receive: Summary of Derivative Instruments That Receive Hedge Accounting Treatment (part 1) Amount of Mark-to-Market Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss) Three Months Ended Derivatives in Cash Flow Hedging Relationship Objective of Hedge Transaction Accounting for Derivative 2019 2018 Currency swaps To protect against changes in cash flows caused by changes in foreign currency exchange rates (exchange rate risk) Unrealized gains and losses are recorded in AOCI and reclassified to interest expense to the extent they are offset by gains and losses on the hedged transaction $ 76 $ (52 ) Summary of Derivative Instruments That Receive Hedge Accounting Treatment (part 2) (1) Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income to Interest Expense Three Months Ended Derivatives in Cash Flow Hedging Relationship 2019 2018 Currency swaps $ 59 $ (18 ) Note (1) There were no amounts excluded from effectiveness testing for any of the periods presented. Based on forecasted foreign currency exchange rates, TVA expects to reclassify approximately $ 15 million of gains from AOCI to interest expense within the next 12 months to offset amounts anticipated to be recorded in interest expense related to exchange gain on the debt.
Summary of Derivative Instruments That Do Not Receive Hedge Accounting Treatment	Summary of Derivative Instruments That Do Not Receive Hedge Accounting Treatment Amount of Gain (Loss) Recognized in Income on Derivatives (1) Three Months Ended December 31 Derivative Type Objective of Derivative Accounting for Derivative Instrument 2019 2018 Interest rate swaps To fix short-term debt variable rate to a fixed rate (interest rate risk) Mark-to-Market gains and losses are recorded as regulatory assets or liabilities $ (21 ) $ (20 ) Commodity contract derivatives To protect against fluctuations in market prices of purchased coal or natural gas (price risk) Mark-to-market gains and losses are recorded as regulatory assets or liabilities Realized gains and losses due to contract settlements are recognized in fuel expense as incurred 1 — Note (1) All of TVA's derivative instruments that do not receive hedge accounting treatment have unrealized gains (losses) that would otherwise be recognized in income but instead are deferred as regulatory assets and liabilities. As such, there were no related gains (losses) recognized in income for these unrealized gains (losses) for the three months ended December 31, 2019 and 2018 .
Fair Value of TVA Derivatives	Fair Values of TVA Derivatives At December 31, 2019 At September 30, 2019 Derivatives That Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Currency swaps £200 million Sterling $ (69 ) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(64) $ (90 ) Accounts payable and £250 million Sterling (27 ) Accounts payable and accrued liabilities $(4); Other long-term liabilities $(23) (61 ) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(56) £150 million Sterling (36 ) Accounts payable and accrued liabilities $(3); Other long-term liabilities $(33) (57 ) Accounts payable and Derivatives That Do Not Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Interest rate swaps $1.0 billion notional $ (1,124 ) Accounts payable and $ (1,261 ) Accounts payable and $476 million notional (436 ) Accounts payable and (498 ) Accounts payable and $42 million notional (5 ) Accounts payable and (5 ) Accounts payable and Commodity contract derivatives (62 ) Other current assets $4; Accounts payable and accrued liabilities $(49); Other long-term liabilities $(17) (41 ) Other current assets $12; Accounts payable and accrued liabilities $(37); Other long-term liabilities $(16)
Commodity Contract Derivatives	Commodity Contract Derivatives At December 31, 2019 At September 30, 2019 Number of Contracts Notional Amount Fair Value (MtM) Number of Contracts Notional Amount Fair Value ( MtM ) Coal contract derivatives 9 10 million tons $ (16 ) 8 9 million tons $ (4 ) Natural gas contract derivatives 53 365 million mmBtu $ (46 ) 65 330 million mmBtu $ (37 )
Offsetting Assets and Liabilities	The amounts of TVA's derivative instruments as reported on the Consolidated Balance Sheets at December 31, 2019 , and September 30, 2019 , are shown in the table below: Derivative Assets and Liabilities (1) At December 31, 2019 At September 30, 2019 Assets Commodity derivatives not subject to master netting or similar arrangement $ 4 $ 12 Liabilities Currency swaps (2) $ 132 $ 208 Interest rate swaps (2) 1,565 1,764 Total derivatives subject to master netting or similar arrangement 1,697 1,972 Commodity derivatives not subject to master netting or similar arrangement 66 53 Total liabilities $ 1,763 $ 2,025 Notes (1) Offsetting amounts primarily include counterparty netting of derivative contracts, margin account deposits for futures commission merchants transactions, and cash collateral received or paid in accordance with the accounting guidance for derivatives and hedging transactions. There were no offsetting amounts on TVA's Consolidated Balance Sheets at either December 31, 2019 or September 30, 2019. (2) Letters of credit of approximately $1.2 billion and $ 1.3 billion were posted as collateral at December 31, 2019 , and September 30, 2019 , respectively, to partially secure the liability positions of one of the currency swaps and one of the interest rate swaps in accordance with the collateral requirements for these derivatives.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Valuation Techniques	The measurement of fair value results in classification into a hierarchy by the inputs used to determine the fair value as follows: Level 1 — Unadjusted quoted prices in active markets accessible by the reporting entity for identical assets or liabilities. Active markets are those in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing. Level 2 — Pricing inputs other than quoted market prices included in Level 1 that are based on observable market data and that are directly or indirectly observable for substantially the full term of the asset or liability. These include quoted market prices for similar assets or liabilities, quoted market prices for identical or similar assets in markets that are not active, adjusted quoted market prices, inputs from observable data such as interest rate and yield curves, volatilities and default rates observable at commonly quoted intervals, and inputs derived from observable market data by correlation or other means. Level 3 — Pricing inputs that are unobservable, or less observable, from objective sources. Unobservable inputs are only to be used to the extent observable inputs are not available. These inputs maintain the concept of an exit price from the perspective of a market participant and should reflect assumptions of other market participants. An entity should consider all market participant assumptions that are available without unreasonable cost and effort. These are given the lowest priority and are generally used in internally developed methodologies to generate management's best estimate of the fair value when no observable market data is available.
Unrealized Investment Gains (Losses)	TVA recorded unrealized gains and losses related to its equity and trading debt securities held during each period as follows: Unrealized Investment Gains (Losses) Three Months Ended Fund Financial Statement Presentation 2019 2018 NDT Regulatory asset $ 111 $ (201 ) ART Regulatory asset 37 (104 ) SERP Other income (expense) 1 (6 ) DCP Other income (expense) 1 (3 )
Fair Value Measurements	Fair Value Measurements Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 509 $ — $ — $ 509 Government debt securities 278 78 — 356 Corporate debt securities — 423 — 423 Mortgage and asset-backed securities — 30 — 30 Institutional mutual funds 266 — — 266 Forward debt securities contracts — 2 — 2 Private credit funds measured at net asset value (1) — — — 52 Private equity funds measured at net asset value (1) — — — 158 Private real asset funds measured at net asset value (1) — — — 142 Commingled funds measured at net asset value (1) — — — 1,225 Total investments 1,053 533 — 3,163 Commodity contract derivatives — 3 1 4 Total $ 1,053 $ 536 $ 1 $ 3,167 Quoted Prices in Active Markets for Identical Liabilities (Level 1) Significant Other Significant Total Liabilities Currency swaps (2) $ — $ 132 $ — $ 132 Interest rate swaps — 1,565 — 1,565 Commodity contract derivatives — 48 18 66 Total $ — $ 1,745 $ 18 $ 1,763 Notes (1) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Consolidated Balance Sheets. (2) TVA records currency swaps net of cash collateral received from or paid to the counterparty, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 14 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . Fair Value Measurements Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 464 $ — $ — $ 464 Government debt securities 279 65 — 344 Corporate debt securities — 417 — 417 Mortgage and asset-backed securities — 32 — 32 Institutional mutual funds 250 — — 250 Forward debt securities contracts — 22 — 22 Private equity funds measured at net asset value (1) — — — 140 Private real estate funds measured at net asset value (1) — — — 135 Private credit measured at net asset value (1) — — — 33 Commingled funds measured at net asset value (1) — — — 1,131 Total investments 993 536 — 2,968 Commodity contract derivatives — 7 5 12 Total $ 993 $ 543 $ 5 $ 2,980 Quoted Prices in Active Markets for Identical Liabilities (Level 1) Significant Other Significant Total Liabilities Currency swaps (2) $ — $ 208 $ — $ 208 Interest rate swaps — 1,764 — 1,764 Commodity contract derivatives — 44 9 53 Total $ — $ 2,016 $ 9 $ 2,025 Notes (1)
Fair Value Measurements Using Significant Unobservable Inputs	The following table presents a reconciliation of all commodity contract derivatives measured at fair value on a recurring basis using significant unobservable inputs (Level 3): Fair Value Measurements Using Significant Unobservable Inputs Commodity Contract Derivatives Three Months Ended Balance at October 1, 2018 $ 58 Change in net unrealized gains (losses) deferred as regulatory assets and liabilities 5 Balance at December 31, 2018 $ 63 Balance at October 1, 2019 $ (4 ) Change in net unrealized gains (losses) deferred as regulatory assets and liabilities (13 ) Balance at December 31, 2019 $ (17 )
Quantitative Information about Level 3 Fair Value Measurements	The following table presents quantitative information related to the significant unobservable inputs used in the measurement of fair value of TVA's assets and liabilities classified as Level 3 in the fair value hierarchy: Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2019 Valuation Technique(s) Unobservable Inputs Range Assets Commodity contract derivatives $ 1 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $95.63/ton Liabilities Commodity contract derivatives 18 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $95.63/ton Quantitative Information about Level 3 Fair Value Measurements Fair Value at September 30, 2019 Valuation Technique(s) Unobservable Inputs Range Assets Commodity contract derivatives $ 5 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $94.51/ton Liabilities Commodity contract derivatives 9 Pricing model Coal supply and demand 0.4 - 0.8 billion tons/year Long-term market prices $12.10 - $94.51/ton
Estimated Values of Financial Instruments Not Recorded at Fair Value	The estimated values of TVA's financial instruments not recorded at fair value at December 31, 2019 , and September 30, 2019 , were as follows: Estimated Values of Financial Instruments Not Recorded at Fair Value At December 31, 2019 At September 30, 2019 Valuation Classification Carrying Fair Carrying Fair EnergyRight ® receivables (including current portion) Level 2 $ 98 $ 97 $ 101 $ 100 Loans and other long-term receivables, net (including current portion) Level 2 135 124 131 120 EnergyRight ® financing obligation (including current portion) Level 2 110 122 113 126 Unfunded loan commitments Level 2 — 8 — 10 Membership interests of VIEs subject to mandatory redemption (including current portion) Level 2 28 36 28 37 Long-term outstanding power bonds (including current maturities), net Level 2 19,970 25,152 20,124 26,059 Long-term debt of VIEs (including current maturities), net Level 2 1,128 1,360 1,128 1,371 Long-term notes payable (including current maturities) Level 2 22 22 23 23

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	3 Months Ended
	Dec. 31, 2019
Other Income and Expenses [Abstract]
Other Income (Expense), Net	17 . Other Income (Expense), Net Income and expenses not related to TVA's operating activities are summarized in the following table: Other Income (Expense), Net Three Months Ended 2019 2018 Bellefonte deposit $ — $ 21 Interest income 5 6 External services 2 3 Gains (losses) on investments 5 (7 ) Miscellaneous — 1 Total Other income (expense), net $ 12 $ 24

Benefit Plans (Tables)

Benefit Plans (Tables)	3 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Components of TVA's Benefit Plans	The components of net periodic benefit cost and other amounts recognized as changes in regulatory assets for the three months ended December 31, 2019 and 2018 , were as follows: Components of TVA's Benefit Plans (1) For the Three Months Ended Pension Benefits Other Post-Retirement Benefits 2019 2018 2019 2018 Service cost $ 12 $ 12 $ 4 $ 3 Interest cost 104 123 4 4 Expected return on plan assets (122 ) (119 ) — — Amortization of prior service credit (24 ) (25 ) (6 ) (6 ) Recognized net actuarial loss 109 82 2 1 Total net periodic benefit cost as actuarially determined 79 73 4 2 Amount expensed (capitalized) due to actions of regulator (2 ) 3 — — Total net periodic benefit cost $ 77 $ 76 $ 4 $ 2

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
State [Table Text Block]	TVA's revenues by state for the three months ended December 31, 2019 and 2018 are detailed in the table below: Operating Revenues By State Three Months Ended December 31 (in millions) 2019 2018 Alabama $ 369 $ 392 Georgia 63 67 Kentucky 157 168 Mississippi 237 251 North Carolina 18 20 Tennessee 1,676 1,771 Virginia 11 12 Subtotal 2,531 2,681 Off-system sales 1 — Revenue from sales of electricity 2,532 2,681 Other revenue 46 44 Total operating revenues $ 2,578 $ 2,725

Revenue Local Power Company Con

Revenue Local Power Company Contracts (Tables)	3 Months Ended
	Dec. 31, 2019
Long-term Contract for Purchase of Electric Power [Line Items]
Long-term Contracts or Programs Disclosure [Text Block]	The number of LPCs with the contract arrangements described below, the revenues derived from such arrangements for the three months ended December 31, 2019 , and the percentage of TVA's total operating revenues for the three months ended December 31, 2019 represented by these revenues are summarized in the tables below: TVA Local Power Company Contracts Contract Arrangements (1) Number of LPCs Revenue from Sales of Electricity to LPCs Percentage of Total Operating Revenues 20-year termination notice 134 $ 1,471 57.1 % 10-year termination notice 4 214 8.3 5-year termination notice 16 672 26.1 Total 154 $ 2,357 91.5 % Note (1) Ordinarily, the LPCs and TVA have the same termination notice period; however, in contracts with three of the LPCs with five-year termination notices, TVA has a 10-year termination notice (which becomes a five-year termination notice if TVA loses its discretionary wholesale rate-setting authority). Certain LPCs have five-year termination notices or a shorter period if any act of Congress, court decision, or regulatory change requires or permits that election.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies General and Basis of Presentation (Details) People in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)People	Dec. 31, 2017USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Mar. 31, 2018USD ($)
Reclassification of Amounts on Cash Flow and Statement of Operations [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 304		$ 299
Restricted Cash and Cash Equivalents	23		23
Regulatory Assets	8,569		8,919
Other Deferred Costs, Net	(10)
Appropriation-investment power program			1,000
Financing Receivable, after Allowance for Credit Loss	$ 124		120
Population of TVA's service area | People	10
Allowance for uncollectible accounts	$ 1		1
Depreciation expense	539	$ 308
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 327		$ 322	$ 322	$ 324

Summary of Significant Accoun_5

Summary of Significant Accounting Policies Allowance for Uncollectible Accounts (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Defined Benefit Plan, Other Cost (Credit)	$ 65	$ 64
Financing Receivable, after Allowance for Credit Loss	124		$ 120
Other Deferred Costs, Net	10
Carrying Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, after Allowance for Credit Loss	$ 135		$ 131

Summary of Significant Accoun_6

Summary of Significant Accounting Policies Leases (Details)	3 Months Ended
	Dec. 31, 2019
Lease obligation related to Purchased Power [Line Items]
Lease obligation related to Purchased Power [Table Text Block]	130

Impact of New Accounting Stan_3

Impact of New Accounting Standards and Interpretations Impact of New Accounting Standards and Interpretations (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Jun. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Restricted cash		$ 13
Reclassification from Operating and maintenance expense to Other income	$ 193

Accounts Receivable, Net (Detai

Accounts Receivable, Net (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Accounts Receivable, Net
Accounts Receivable, before Allowance for Credit Loss, Current	$ 1,326	$ 1,624
Other receivables	101	115
Allowance for uncollectible accounts	1	1
Accounts receivable, net	$ 1,427	$ 1,739

Inventories, Net (Details)

Inventories, Net (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Inventories, Net
Materials and supplies inventory	$ 752	$ 742
Fuel inventory	337	294
Renewable energy certificates/emission allowance inventory, net	17	16
Allowance for inventory obsolescence	(54)	(53)
Inventories, net	$ 1,052	$ 999

Other Long-Term Assets (Details

Other Long-Term Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019
Other Long-Term Assets
EnergyRight® receivables	$ 97	$ 100
Prepaid Expense, Noncurrent	29	22
Restricted Cash and Cash Equivalents	23	23
Total other long-term assets	334	325
Prepaid Expense, Current	7	5
Other long-term assets
Other Long-Term Assets
Loans and other long-term receivables, net	129	125
EnergyRight® receivables	78	81
Prepaid capacity payments	17	19
Other	58	55
Restricted Cash and Cash Equivalents, Noncurrent		$ 23
Accounts Receivable
Other Long-Term Assets
EnergyRight® receivables	$ 20
Energy Right
Other Long-Term Assets
Number of days in default	180 days
Energy Right | Minimum
Other Long-Term Assets
Debt Instrument, Term	5 years
Energy Right | Maximum
Other Long-Term Assets
Debt Instrument, Term	10 years

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Regulatory Assets and Liabilities
Current regulatory assets	$ 159	$ 156
Non-current regulatory assets	8,410	8,763
Regulatory assets	8,569	8,919
Current regulatory liabilities	137	150
Regulatory Liability, Noncurrent	1
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	134	138
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	3	12
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Current regulatory assets	89	89
Non-current regulatory assets	1,074	1,241
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	49	39
Non-current regulatory assets	17	15
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets	21	28
Deferred pension costs and other post-retirement benefits costs
Regulatory Assets and Liabilities
Non-current regulatory assets	4,678	4,756
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	765	868
Environmental agreements
Regulatory Assets and Liabilities
Non-current regulatory assets	1,725	1,741
Other non-current regulatory assets
Regulatory Assets and Liabilities
Non-current regulatory assets	$ 151	$ 142

Variable Interest Entities Vari

Variable Interest Entities Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2018	Sep. 30, 2013	Sep. 30, 2012
Variable Interest Entities
Accrued interest	$ 24	$ 11
VIE Financing
Construction management agreement and lease		1,167	$ 1,180		$ 1,000
Face amount	$ 40
Financial instruments subject to mandatory redemption, interest rate, stated percentage	7.00%
Liabilities
Current maturities of long-term debt of variable interest entities	$ 39	39
Long-term debt of variable interest entities, net	1,089	1,089
Interest Expense	14
SCCG
VIE Financing
Face amount				$ 360
Debt and Lease Obligation				$ 400
JSCCG
VIE Financing
Face amount					900
Holdco
VIE Financing
Face amount					$ 100
Accounts payable and accrued liabilities
VIE Financing
Construction management agreement and lease	3	3
Total current liabilities
VIE Financing
Construction management agreement and lease		53	$ 66
Other long-term liabilities
VIE Financing
Construction management agreement and lease	$ 25	$ 25

Other Long-Term Liabilities (De

Other Long-Term Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2019	Sep. 30, 2019
Other Long-Term Liabilities
Finance Lease, Liability		$ 180	$ 182
Pipeline financing obligation		79	80
Interest rate swap liabilities		1,565	1,764
Increase in Interest rate Derivative Liabilities, at Fair Value		199
Capital lease obligations		223	223
Currency swap liabilities	[1]	132	208
EnergyRight® financing obligation		122	126
Total other long-term liabilities		2,201	2,490
Regulatory Liability, Noncurrent		1
Accounts Payable and Accrued Liabilities
Other Long-Term Liabilities
Finance Lease, Liability		1
Obligations under long-term service agreements		14	12
Interest rate swap liabilities		89	88
EnergyRight® financing obligation		22	23
Other long-term liabilities
Other Long-Term Liabilities
Obligations under long-term service agreements		61	66
Interest rate swap liabilities		1,477	1,676
Currency swap liabilities		120	193
EnergyRight® financing obligation		88	90
Other		$ 196	$ 203
[1]	TVA records currency swaps net of cash collateral received from or paid to the counterparty, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 14 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities.

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)
Asset Retirement Obligations
Asset Retirement Obligation, Period Increase (Decrease)	$ 135
Amortization and Depreciation of Decontaminating and Decommissioning Assets	42
Balance at September 30, 2019	5,616
Settlements	(32)
Asset Retirement Obligation, Revision of Estimate	117
Accretion (recorded as regulatory asset)	50
Balance at December 31, 2019	5,751
Non-nuclear Operating
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate	38
Nuclear
Asset Retirement Obligations
Balance at September 30, 2019	3,136
Settlements	0
Asset Retirement Obligation, Revision of Estimate	0
Accretion (recorded as regulatory asset)	35
Balance at December 31, 2019	3,171
Non-nuclear
Asset Retirement Obligations
Balance at September 30, 2019	2,480
Settlements	(32)
Asset Retirement Obligation, Revision of Estimate	117
Accretion (recorded as regulatory asset)	15
Balance at December 31, 2019	2,580
Asset Retirement Obligation, Revision of Estimate	129
Non-nuclear Closed Activities
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate	91
Accounts payable and accrued liabilities
Asset Retirement Obligations
Current portion of ARO	$ (163)

Debt and Other Obligations Debt

Debt and Other Obligations Debt Outstanding (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Sep. 30, 2019
Debt Instrument
Interest Expense		$ 14
Short-term debt
Short-term debt, net		895	$ 922
Current maturities of power bonds		1,029	1,030
Current maturities of long-term debt of variable interest entities		39	39
Current maturities of notes payable		22	23
Total current debt outstanding, net		1,985	2,014
Long-term debt
Long-term power bonds	[1]	19,065	19,225
Long-term debt of variable interest entities		1,089	1,089
Long-term notes payable		1
Unamortized discounts, premiums, issues costs, and other		(124)	(131)
Total long-term debt, net		20,030	20,183
Total outstanding debt		$ 22,015	$ 22,197
[1]	Includes net exchange gain from currency transactions of $133 million and $191 million at December 31, 2019, and September 30, 2019, respec

Debt and Other Obligations De_2

Debt and Other Obligations Debt Securities Activity (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Debt Instrument
Long-term notes payable		$ 1
Total long-term debt, net		20,030		$ 20,183
Redemptions/maturities of power bonds		218	$ 1,002
Total redemptions/maturities of debt	[1]	(218)
electronotes [Member]
Debt Instrument
Redemptions/maturities of power bonds		217
2009 Series B [Member]
Debt Instrument
Redemptions/maturities of power bonds		1
2013 Series A [Member]
Debt Instrument
Redemptions/maturities of power bonds
Total
Debt Instrument
Percent of par value		100.00%
electronotes [Member]
Debt Instrument
Debt Instrument, Interest Rate, Effective Percentage		0.00%
2009 Series B [Member]
Debt Instrument
Debt Instrument, Interest Rate, Effective Percentage		0.00%
[1]	(1) Amounts for notes payable were less than$1 million at December 31, 2019, and are therefore not represented in the table above.(2) All redemptions were at 100 percent of par.

Debt and Other Obligations Cred

Debt and Other Obligations Credit Facility Agreements (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)Credit_facilities	Sep. 30, 2019USD ($)
Line of Credit Facility [Line Items]
Summary of Long-Term Credit Facilities	The following table provides additional information regarding TVA's funding available under the four long-term revolving credit facilities: Summary of Long-Term Credit Facilities At December 31, 2019 Maturity Date Facility Limit Letters of Credit Outstanding Cash Borrowings Availability December 2021 $ 150 $ 38 $ — $ 112 February 2022 500 500 — — June 2023 1,000 342 — 658 September 2023 1,000 310 — 690 Total $ 2,650 $ 1,190 $ — $ 1,460
Line of Credit
Line of Credit Facility [Line Items]
Current borrowing capacity for credit facilities	$ 150
Total Cash Borrowings for Credit Facilities	0
Revolving Credit Facilities
Line of Credit Facility [Line Items]
Current borrowing capacity for credit facilities	$ 2,700
Number of revolving credit facilities | Credit_facilities	4
December 2019 Credit Facility	$ 150
February 2022 Credit Facility	500
June 2020 Credit Facility	1,000
September 2020 Credit Facility	1,000
Cash Borrowings-December 2019 Credit Facility	0
Cash Borrowings-February 2022 Credit Facility	0
Cash Borrowings-June 2020 Credit Facility	0
Cash Borrowings-September 2020 Credit Facility	0
Total Cash Borrowings for Credit Facilities	0
Remaining Availability, December 2019 Credit Facility	112
Remaining Availability, February 2022 Credit Facility	0
Remaining Availability, June 2020 Credit Facility	658
Remaining Availability, September 2020 Credit Facility	690
Total Remaining Availability for Credit Facilities	1,460
Letter of Credit
Line of Credit Facility [Line Items]
Letter of Credit Outstanding, December 2019 Credit Facility	38
Letter of Credit Outstanding, February 2022 Credit Facility	500
Letter of Credit Outstanding, June 2020 Credit Facility	342
Letter of Credit Outstanding, September 2020 Credit Facility	310
Amount of letters of credit outstanding for credit facilities	$ 1,200	$ 1,300

Debt and Other Obligations Leas

Debt and Other Obligations Lease/Leaseback Obligations (Details) $ in Millions	Dec. 31, 2019USD ($)	Sep. 30, 2019
Sale Leaseback Transaction [Line Items]
Leasing transaction, number of units		24
CT and QTE outstanding leaseback obligation	$ 263

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Gain), Reclassification Adjustment from AOCI		$ 59
Reclassification to earnings from cash flow hedges	[1]	$ (59)	$ 18
[1]	There were no amounts excluded from effectiveness testing for any of the periods presented. Based on forecasted foreign currency exchange rates, TVA expects to reclassify approximately $15 million of gains from AOCI to interest expense within the next 12 months to offset amounts anticipated to be recorded in interest expense related to exchange gain on the debt.

Risk Management Activities an_3

Risk Management Activities and Derivative Transactions Derivative Instruments That Receive Hedge Accounting Treatment (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Summary of Derivative Instruments That Receive Hedge Accounting Treatment
Net unrealized gain (loss) on cash flow hedges		$ 76	$ (52)
Reclassification to earnings from cash flow hedges	[1]	(59)	$ 18
Reclassification to earnings from cash flow hedges in the next 12 months		$ (15)
[1]	There were no amounts excluded from effectiveness testing for any of the periods presented. Based on forecasted foreign currency exchange rates, TVA expects to reclassify approximately $15 million of gains from AOCI to interest expense within the next 12 months to offset amounts anticipated to be recorded in interest expense related to exchange gain on the debt.

Risk Management Activities an_4

Risk Management Activities and Derivative Transactions Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details)		3 Months Ended
		Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)
Derivative
Amount recognized for unrealized gains (losses)		$ 0
Change in Unrealized gains (losses) on Interest Rate Derivatives		171,000,000	$ 110,000,000
Interest Rate Swap
Derivative
Gain (loss) recognized in income on derivatives	[1]	(21,000,000)	(20,000,000)
Fair value		(436,000,000)		$ (498,000,000)
Commodity Contract Derivatives
Derivative
Gain (loss) recognized in income on derivatives	[1]	1,000,000	$ 0
Fair value		$ (62,000,000)		$ (41,000,000)
Coal Contract Derivatives
Derivative
Number of contracts		9		8
Derivative, Nonmonetary Notional Amount		10,000,000		9,000,000
Fair value		$ (16,000,000)		$ (4,000,000)
Natural gas contract derivatives
Derivative
Number of contracts		53		65
Derivative, Nonmonetary Notional Amount		365,000,000		330,000,000
Fair value		$ (46,000,000)		$ (37,000,000)
[1]	All of TVA's derivative instruments that do not receive hedge accounting treatment have unrealized gains (losses) that would otherwise be recognized in income but instead are deferred as regulatory assets and liabilities. As such, there were no related gains (losses) recognized in income for these unrealized gains (losses) for the three months ended December 31, 2019 and 2018.

Risk Management Activities an_5

Risk Management Activities and Derivative Transactions Fair Values of TVA Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Derivatives, Fair Value
Gross amounts of recognized liabilities	$ 1,697	$ 1,972
200 million Sterling currency swap
Derivatives, Fair Value
Fair value	(69)	(90)
Gross amounts of recognized liabilities	132	208
200 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(64)	(84)
200 million Sterling currency swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(5)	(6)
250 million Sterling currency swap
Derivatives, Fair Value
Fair value	(27)	(61)
250 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(23)	(56)
250 million Sterling currency swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(5)	(5)
150 million Sterling currency swap
Derivatives, Fair Value
Fair value	(36)	(57)
150 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(33)	(53)
150 million Sterling currency swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(3)	(4)
$1.0 billion notional interest rate swap
Derivatives, Fair Value
Fair value	(1,124)	(1,261)
$1.0 billion notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(1,061)	(1,199)
$1.0 billion notional interest rate swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(63)	(62)
$476 million notional interest rate swap
Derivatives, Fair Value
Fair value	(436)	(498)
$476 million notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(413)	(474)
$476 million notional interest rate swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(23)	(24)
$42 million notional interest rate swap
Derivatives, Fair Value
Fair value	(5)	(5)
$42 million notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(3)	(3)
$42 million notional interest rate swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(2)	(2)
Commodity contract derivatives
Derivatives, Fair Value
Fair value	(62)	(41)
Commodity contract derivatives | Other long-term assets
Derivatives, Fair Value
Fair value	0	0
Commodity contract derivatives | Other current assets
Derivatives, Fair Value
Fair value	4	12
Commodity contract derivatives | Other long-term liabilities
Derivatives, Fair Value
Fair value	(17)	(16)
Commodity contract derivatives | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	$ (49)	$ (37)

Risk Management Activities an_6

Risk Management Activities and Derivative Transactions Currency Swaps Outstanding (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)Bond_issues	Jun. 30, 2019Bond_issues
Derivative
Number of British pound sterling denominated bond transactions	3
Number of currency swaps outstanding		3
Associated TVA bond issues currency exposure | $	$ 600
Minimum
Derivative
Expiration date range of swaps	2021
Maximum
Derivative
Expiration date range of swaps	2043

Risk Management Activities an_7

Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22
Coal Contract
Derivative
Fair value	(16)	(4)
Natural Gas Contract Derivatives
Derivative
Fair value	(46)	(37)
Fair Value, Inputs, Level 2
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22

Risk Management Activities an_8

Risk Management Activities and Derivative Transactions Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Offsetting Assets [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	$ 1,763	$ 2,025
Gross amounts of recognized liabilities	1,697	1,972
Total derivatives not subject to master netting or similar arrangement	4	12
Forward Contract Derivative Asset, at Fair Value	2	22
Derivative Liability, Not Subject to Master Netting Arrangement	66	53
Letter of Credit
Offsetting Assets [Line Items]
Amount of letters of credit outstanding for credit facilities	1,200	1,300
Currency Swap
Offsetting Assets [Line Items]
Gross amounts of recognized liabilities	132	208
Interest Rate Contract
Offsetting Assets [Line Items]
Gross amounts of recognized liabilities	1,565	1,764
Fair Value, Inputs, Level 2
Offsetting Assets [Line Items]
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22

Risk Management Activities an_9

Risk Management Activities and Derivative Transactions Offsetting for Derivative Liabilities (Details) $ in Millions	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019Bond_issues
Offsetting Liabilities [Line Items]
Number of currency swaps outstanding | Bond_issues			3
Accounts Receivable, before Allowance for Credit Loss, Current	$ 1,326	$ 1,624
Total derivatives not subject to master netting or similar arrangement	4	12
Gross amounts of recognized liabilities	1,697	1,972
Derivative Liability, Not Subject to Master Netting Arrangement	66	53
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	1,763	2,025
Forward Contract Derivative Asset, at Fair Value	2	22
Currency Swap
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	132	208
Interest Rate Contract
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	1,565	1,764
Letter of Credit
Offsetting Liabilities [Line Items]
Amount of letters of credit outstanding	1,200	1,300
Fair Value, Inputs, Level 2
Offsetting Liabilities [Line Items]
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22

Risk Management Activities a_10

Risk Management Activities and Derivative Transactions Collateral (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22
Likely cash collateral obligation increase	22
Collateralized Securities [Member]
Derivative
Derivative, Net Liability Position, Aggregate Fair Value	1,700
Derivative, Collateral, Right to Reclaim Cash	1,200
Letter of Credit
Derivative
Amount of letters of credit outstanding	1,200	1,300
Fair Value, Inputs, Level 2
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 22

Risk Management Activities a_11

Risk Management Activities and Derivative Transactions Counterparty Credit Risk (Details) $ in Millions	Dec. 31, 2019USD ($)megawatts	Sep. 30, 2019USD ($)
Derivative
Total derivatives not subject to master netting or similar arrangement | $	$ 4	$ 12
Long-term Contract for Purchase of Electric Power [Domain]
Derivative
Megawatts | megawatts	440

Risk Management Activities a_12

Risk Management Activities and Derivative Transactions Cash Flow from Hedging (Details) $ in Millions	Dec. 31, 2019USD ($)
Cash Flow from Hedging [Abstract]
Associated bond issues currency exposure	$ 600

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements - Investments (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)
Investment Gains (Losses)
Financing Receivable, after Allowance for Credit Loss	$ 124		$ 120
Balance in NDT	2,300
Balance in ART	$ 815
Period of time where the investor contributes capital to an investment in a private partnership - minimum	three
Period of time where the investor contributes capital to an investment in a private partnership - maximum	four
Minimum investment period	10 years
Number of readily available quoted exchange prices for the investments	0
LTDCP [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	$ 1	$ (3)
SERP
Investment Gains (Losses)
Unrealized gains (losses) on investments	1	(6)
ART [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	37	(104)
NDT [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	111	$ (201)
Equity Funds
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	208
Real Estate Funds
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	57
Credit [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	10
Private Equity Funds [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	103
Private real estate funds [Member]
Investment Gains (Losses)
Fair value plan assets gross	41
Private Credit [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	$ 5

Fair Value Measurements Fair _2

Fair Value Measurements Fair Value Measurements - Nonperformance Risk (Details) $ in Millions	Dec. 31, 2019USD ($)
Nonperformance Risk
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 1

Fair Value Measurements Fair _3

Fair Value Measurements Fair Value Measurements (Details) - USD ($) $ in Millions		Dec. 31, 2019	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financing Receivable, after Allowance for Credit Loss		$ 124	$ 120
Investments
Equity securities		509	464
Government debt securities		356	344
Corporate debt securities		423	417
Mortgage and asset-backed securities		30	32
Institutional mutual funds		266	250
Forward debt securities contracts		2	22
Private credit measured at net asset value		52
Private equity funds measured at net asset value(1)		158	140	[1]
Private real estate funds measured at net asset value(1)		142	135	[1]
Commingled funds measured at net asset value(1)		1,225	1,131	[1]
Total investments		3,163	2,968
Commodity contract derivatives		4	12
Total		3,167	2,980
Liabilities
Currency swaps	[2]	132	208
Interest rate swaps		1,565	1,764
Commodity contract derivatives		66	53
Total		1,763	2,025
Fair Value, Inputs, Level 1
Investments
Equity securities		509	464
Government debt securities		278	279
Corporate debt securities		0	0
Mortgage and asset-backed securities		0	0
Institutional mutual funds		266	250
Forward debt securities contracts		0	0
Private credit measured at net asset value		0
Private equity funds measured at net asset value(1)		0	0	[1]
Private real estate funds measured at net asset value(1)		0	0	[1]
Commingled funds measured at net asset value(1)		0	0	[1]
Total investments		1,053	993
Commodity contract derivatives		0	0
Total		1,053	993
Liabilities
Currency swaps		0	0	[2]
Interest rate swaps		0	0
Commodity contract derivatives		0	0
Total		0	0
Fair Value, Inputs, Level 2
Investments
Equity securities		0	0
Government debt securities		78	65
Corporate debt securities		423	417
Mortgage and asset-backed securities		30	32
Institutional mutual funds		0	0
Forward debt securities contracts		2	22
Private credit measured at net asset value		0
Private equity funds measured at net asset value(1)		0	0	[1]
Private real estate funds measured at net asset value(1)		0	0	[1]
Commingled funds measured at net asset value(1)		0	0	[1]
Total investments		533	536
Commodity contract derivatives		3	7
Total		536	543
Liabilities
Currency swaps		132	208	[2]
Interest rate swaps		1,565	1,764
Commodity contract derivatives		48	44
Total		1,745	2,016
Fair Value, Inputs, Level 3
Investments
Equity securities		0	0
Government debt securities		0	0
Corporate debt securities		0	0
Mortgage and asset-backed securities		0	0
Institutional mutual funds		0	0
Forward debt securities contracts		0	0
Private credit measured at net asset value		0
Private equity funds measured at net asset value(1)		0	0	[1]
Private real estate funds measured at net asset value(1)		0	0	[1]
Commingled funds measured at net asset value(1)		0	0	[1]
Total investments		0	0
Commodity contract derivatives		1	5
Total		1	5
Liabilities
Currency swaps		0	0	[2]
Interest rate swaps		0	0
Commodity contract derivatives		18	9
Total		$ 18	$ 9
[1]	Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Consolidated Balance Sheets.
[2]	TVA records currency swaps net of cash collateral received from or paid to the counterparty, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 14 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities.

Fair Value Measurements Fair _4

Fair Value Measurements Fair Value Measurements Using Significant Unobservable Inputs (Details) tons-per-year in Billions	3 Months Ended
	Dec. 31, 2019USD ($)tons-per-year	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)tons-per-year	Mar. 31, 2018USD ($)	Sep. 30, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contract derivatives	$ 4,000,000		$ 12,000,000
Commodity contract derivatives	$ 66,000,000		$ 53,000,000
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurements tons per year | tons-per-year	0.8		0.8
Price per ton	$ 112.64		$ 112.24
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurements tons per year | tons-per-year	0.7		0.7
Price per ton	$ 12.25		$ 12.25
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contract derivatives	1,000,000		5,000,000
Commodity contract derivatives	18,000,000		9,000,000
Commodity Contract Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance	(17,000,000)		$ (4,000,000)	$ 63,000,000	$ 58,000,000
Net unrealized gains (losses) deferred as regulatory assets and liabilities	$ (13,000,000)	$ 5,000,000

Fair Value Measurements Estimat

Fair Value Measurements Estimated Values of Financial Instruments Not Recorded at Fair Value (Details) - USD ($)	Dec. 31, 2019	Sep. 30, 2019
Carrying Value
Estimated Values of Financial Intruments Not Recorded at Fair Value
EnergyRight® receivables (including current portion)	$ 98,000,000	$ 101,000,000
Loans and other long-term receivables, net (including current portion)	135,000,000	131,000,000
EnergyRight® financing obligation (including current portion)	110,000,000	113,000,000
Unfunded loan commitments	0	0
Membership interests of VIEs subject to mandatory redemption (including current portion)	28,000,000	28,000,000
Long-term outstanding power bonds (including current maturities), net	19,970,000,000	20,124,000,000
Long-term debt of VIEs (including current maturities), net	1,128,000,000	1,128,000,000
Long-term notes payable (including current maturities)	22,000,000	23,000,000
EnergyRight® receivables (including current portion)	97,000,000	100,000,000
Loans and other long-term receivables, net (including current portion)	124,000,000	120,000,000
EnergyRight® financing obligation (including current portion)	122,000,000	126,000,000
Unfunded loan commitments	8,000,000	10,000,000
Membership interests of VIEs subject to mandatory redemption (including current portion)	36,000,000	37,000,000
Long-term outstanding power bonds (including current maturities), net	25,152,000,000	26,059,000,000
Long-term debt of VIEs (including current maturities), net	1,360,000,000	1,371,000,000
Long-term notes payable (including current maturities)	$ 22	$ 23,000,000

Other Income (Expense), Net (De

Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Income (Expense), Net
Deposit Liabilities, Description	-420892		21
External services	$ 2		$ 3
Interest income	5		6
Gains (losses) on investments	5	$ 7	(7)
Miscellaneous	0		1
Total other income (expense), net	12	$ 24	$ 24
Increase in Other Income/Expense	12
Increase in Gains (Losses)	$ 21

Benefit Plans Components of Ben

Benefit Plans Components of Benefit Plans (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)plans	Dec. 31, 2017USD ($)
Retirement Plan Disclosure
Number of unfunded post-retirement health care plans | plans	2
Pension Plan
Retirement Plan Disclosure
Service cost	$ 12	$ 12
Interest cost	104	123
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(122)	119
Amortization of prior service cost	(24)	(25)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	109	(82)
Net periodic benefit cost as acutarially determined	79	73
Amount capitalized due to actions of regulator	(2)	(3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	77	76
Other Postretirement Benefit Plan
Retirement Plan Disclosure
Service cost	4	3
Interest cost	4	4
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0
Amortization of prior service cost	(6)	(6)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	2	(1)
Net periodic benefit cost as acutarially determined	4	2
Amount capitalized due to actions of regulator	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 4	$ 2

Benefit Plans Components of Net

Benefit Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2017
Other Pension Plan
Retirement Plan Disclosure
Defined benefit plan contributions	$ 75
Pension Benefits
Retirement Plan Disclosure
Service cost	12	$ 12
Interest cost	104	123
Expected return on plan assets	122	(119)
Amortization of prior service cost	(24)	(25)
Recognized net actuarial loss	(109)	82
Total net periodic benefit cost as actuarially determined	79	73
Amount capitalized due to actions of regulator	2	3
Total net periodic benefit cost	77	76
Other Post-retirement Benefits
Retirement Plan Disclosure
Defined benefit plan contributions	10
Service cost	4	3
Interest cost	4	4
Expected return on plan assets	0	0
Amortization of prior service cost	(6)	(6)
Recognized net actuarial loss	(2)	1
Total net periodic benefit cost as actuarially determined	4	2
Amount capitalized due to actions of regulator	0	0
Total net periodic benefit cost	$ 4	$ 2

Benefit Plans Contributions (De

Benefit Plans Contributions (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)
Retirement Plan Disclosure
Remaining Employer Contributions	$ 225
Contributions to 401K	24
Other Pension Plan
Retirement Plan Disclosure
Defined benefit plan contributions	75
defined benefit plan, plan assets, monthly contributions by employer	25
Other Post-retirement Benefits
Retirement Plan Disclosure
Defined benefit plan contributions	10
SERP
Retirement Plan Disclosure
Defined benefit plan contributions	5
Minimum | Other Pension Plan
Retirement Plan Disclosure
Defined benefit plan contributions	$ 300

Contingencies and Legal Proce_2

Contingencies and Legal Proceedings Contingencies (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)Proceduresreactors	Sep. 30, 2019USD ($)
Loss Contingencies
Nuclear liability insurance	$ 450
Assessment from licensees for each licensed reactor	$ 138
Number of licensed reactors in US | reactors	98
Nuclear accident assessment limitation per year per unit	$ 20
Maximum assessment per nuclear incident	963
Total amount of protection available	14,000
Amount of insurance available for loss at any one site	2,100
Maximum amount of retrospective premiums	139
Maximum idemnity if a covered accident takes or keeps a nuclear unit offline	490
Maximum retrospective premiums	46
Estimated future decommissioning cost	$ 5,751	$ 5,616
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures	2
Possible additional future costs for compliance with Clean Air Act requirements	$ 132
Possible additional future costs for compliance with CCR requirements	1,117
Possible additional future costs for compliance with Clean Water requirements.	261
Estimated liability for cleanup and environmental work	13	15
Nuclear
Loss Contingencies
Estimated future decommissioning cost	3,171	3,136
Non-nuclear
Loss Contingencies
Estimated future decommissioning cost	$ 2,580	$ 2,480

Contingencies and Legal Proce_3

Contingencies and Legal Proceedings Legal Proceedings (Details)	3 Months Ended
	Dec. 31, 2019USD ($)megawattsUnitsGroupsAgreements	Sep. 30, 2019USD ($)
Legal Proceedings
Number of licensed nuclear units | Units	7
Amount paid for remediation under amended consent decree		$ 100,000
General
Legal Proceedings
Legal loss contingency accrual	$ 13,000,000
Environmental Agreements
Legal Proceedings
Number of similar environmental agreements entered into | Agreements	2
Number of environmental agreements entered into with the EPA | Agreements	1
Number of environmental agreements entered into with environmental advocacy groups | Groups	3
Number of units to be idled | Units	18
Megawatts | megawatts	2,200
Megawatts option 2	3,500
Amount to be invested in certain TVA environmental projects	$ 290,000,000
Amount to be provided to fund environmental projects	60,000,000
Amount to pay civil penalties	$ 10,000,000

Subsequent Event (Details)

Subsequent Event (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Redemptions/maturities of power bonds	$ 218	$ 1,002

Gallatin Coal Combustion Residu

Gallatin Coal Combustion Residual Facilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Other Long-Term Liabilities
Current regulatory assets	$ 159	$ 156

Revenue (Details)

Revenue (Details)	3 Months Ended
	Dec. 31, 2019USD ($)percentnumber_of_local_power_companies	Dec. 31, 2018USD ($)
State [Line Items]
Electric revenue	$ (2,531,000,000)	$ (2,681,000,000)
Sales of Electricity	2,532,000,000	2,681,000,000
Off System Sales of Electricity	1,000,000	0
Other revenue	$ 46,000,000	44,000,000
Total number of customers	154
Total long duration contract revenue recognition	2,357,000,000
Total number of customers that represent a percent of sales | percent	1
Revenues	$ 2,578,000,000	2,725,000,000
ALABAMA
State [Line Items]
Electric revenue	(369,000,000)	(392,000,000)
GEORGIA
State [Line Items]
Electric revenue	(63,000,000)	(67,000,000)
KENTUCKY
State [Line Items]
Electric revenue	(157,000,000)	(168,000,000)
MISSISSIPPI
State [Line Items]
Electric revenue	(237,000,000)	(251,000,000)
NORTH CAROLINA
State [Line Items]
Electric revenue	(18,000,000)	(20,000,000)
TENNESSEE
State [Line Items]
Electric revenue	(1,676,000,000)	(1,771,000,000)
VIRGINIA
State [Line Items]
Electric revenue	$ (11,000,000)	$ (12,000,000)
20-year Termination Notice [Member]
State [Line Items]
Number of customers | number_of_local_power_companies	134
Number of customers that represent the percent of sales | percent	1
Revenues	$ 1,471,000,000
10-year Termination Notice [Member]
State [Line Items]
Number of customers | number_of_local_power_companies	4
Number of customers that represent the percent of sales | percent	0
Revenues	$ 214,000,000
5-year termination notice [Member]
State [Line Items]
Number of customers | number_of_local_power_companies	16
Number of customers that represent the percent of sales | percent	0
Revenues	$ 672,000,000

Revenue Customer Type (Details)

Revenue Customer Type (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue, Major Customer [Line Items]
MLGW's % of operating revenues	800.00%
Sales of Electricity	$ 2,532	$ 2,681
Electric revenue	2,531	2,681
Other revenue	46	44
Revenues	2,578	2,725
lpcs [Domain]
Revenue, Major Customer [Line Items]
Electric revenue	2,357	2,468
industries directly served [Domain]
Revenue, Major Customer [Line Items]
Electric revenue	150	184
federal agencies and other [Domain]
Revenue, Major Customer [Line Items]
Electric revenue	$ 25	$ 29

Revenue Unpaid Incentives (Deta

Revenue Unpaid Incentives (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Paid Economic Incentives	$ 76	$ 67
Unpaid Economic Incentives	$ 158		$ 157

Revenue Local Power Company C_2

Revenue Local Power Company Contracts (Details)	3 Months Ended
	Dec. 31, 2019USD ($)percentnumber_of_local_power_companies	Dec. 31, 2018USD ($)
Long-term Contract for Purchase of Electric Power [Line Items]
Total number of customers	154
Long-Duration Contracts Revenue Recognition, Policy [Policy Text Block]	$ 2,578,000,000	$ 2,725,000,000
Total number of customers that represent the percent of sales | percent	1
Total long-duration contracts revenue recognition	2,357,000,000
5-year Termination Notice [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Number of customers | number_of_local_power_companies	16
Number of customers that represent the percent of sales | percent	0
Long-Duration Contracts Revenue Recognition, Policy [Policy Text Block]	$ 672,000,000
10-year Termination Notice [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Number of customers | number_of_local_power_companies	4
Number of customers that represent the percent of sales | percent	0
Long-Duration Contracts Revenue Recognition, Policy [Policy Text Block]	$ 214,000,000
20-year Termination Notice [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Number of customers | number_of_local_power_companies	134
Number of customers that represent the percent of sales | percent	1
Long-Duration Contracts Revenue Recognition, Policy [Policy Text Block]	$ 1,471,000,000

Plant Closures (Details)

Plant Closures (Details) - Property, Plant and Equipment [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Dispositions	4	155
Property, Plant and Equipment, Disposals	$ 19
Depreciation expense	$ 225	$ 791

Leases (Details)

Leases (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Oct. 01, 2019	Sep. 30, 2019
Amounts Recognized on TVA's Consolidated Balance Sheet [Line Items]
Operating lease assets, net of amortization	$ 192
Finance lease, asset	143
Lease assets	335
Operating Lease, Liability, Current	72		$ 0
Finance Lease, Liability, Current	6
Operating Lease, Liability, Noncurrent	130
Finance Lease, Liability, Noncurrent	180
Lease liabilities	388
Operating Lease, Asset		$ 205
Operating Lease, Liability		$ 210
Short-term Lease, Cost	1
Operating Leases, Rent Expense	$ 18

Leases Lease Costs (Details)

Leases Lease Costs (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating Lease, Cost	$ 18
Variable Lease, Cost	6
Finance lease, amortization expense	2
Finance Lease, Interest Expense	6
Finance lease expenses	8
Lease, Cost	$ 32

Leases Amounts Recognized on TV

Leases Amounts Recognized on TVA's Consolidated Statements of Cash Flows (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)
Amounts Recognized on TVA's Consolidated Statements of Cash Flows [Abstract]
Operating cash flows for operating leases	$ 14
Operating cash flows for finance leases	6
Financing cash flows for finance leases	1
Lease assets obtained in exchange for lease obligations (non-cash) - Operating	4
Lease assets obtained in exchange for lease obligations (non-cash) - Finance	$ 0

Leases Future Minimum Lease Pay

Leases Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Amounts Recognized on TVA's Consolidated Statements of Cash Flows [Abstract]
Operating Leases, Future Minimum Payments, Remainder of Fiscal Year	$ 61	$ 76
Operating Leases, Future Minimum Payments Due, Next Twelve Months	74	75
Operating Leases, Future Minimum Payments, Due in Four Years	2	3
Operating Leases, Future Minimum Payments, Due Thereafter		2
Operating Leases, Future Minimum Payments Due	207	228
Present value of future minimum lease payments, operating leases	(5)	0
Operating present value of net minimum lease payments	202	228
Operating Leases, Future Minimum Payments, Due in Two Years	59	60
Operating Leases, Future Minimum Payments, Due in Three Years	11	12
Finance Lease, Liability, Payments, Remainder of Fiscal Year	40	53
Finance Lease, Liability, Payments, Due Next Twelve Months	53	53
Finance Lease, Liability, Payments, Due Year Two	53	53
Finance Lease, Liability, Payments, Due Year Three	55	55
Finance Lease, Liability, Payments, Due Year Four	51	51
Finance Lease, Liability, Payments, Due Thereafter	418	418
Finance Lease, Liability, Payment, Due	670	683
Finance Lease, Liability, Payments, Amount representing interest	(484)	(495)
Finance present value of net minimum lease payments	$ 186	$ 188