Tennessee Valley Authority PARRS D 2028 (TVC) 10-K 17 Nov 20 2020 FY Annual report Financial data

DEI Document

DEI Document shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)shares
Document Information [Line Items]
Entity Registrant Name	TENNESSEE VALLEY AUTHORITY
Entity Central Index Key	0001376986
Current Fiscal Year End Date	--09-30
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding | shares	0
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float | $	$ 0
Document Transition Report	false
Entity File Number	000-52313
Entity Tax Identification Number	62-0474417
Entity Address, State or Province	TN
Entity Address, City or Town	Knoxville
Entity Address, Address Line One	400 W. Summit Hill Drive
Local Phone Number	632-2101
City Area Code	(865)
Entity Address, Postal Zip Code	37902 (Zip Code)
Entity Interactive Data Current	Yes
ICFR Auditor Attestation Flag	true

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating revenues
Electric revenue	$ 10,104	$ 11,159	$ 11,075
Other revenue	145	159	158
Revenue from sales of electricity	10,249	11,318	11,233
Operating expenses
Fuel	1,584	1,896	2,049
Purchased power	880	1,007	973
Operating and maintenance	2,720	3,090	2,598
Depreciation and amortization	1,826	1,973	2,527
Tax equivalents	528	541	518
Total operating expenses	7,538	8,507	8,665
Operating income	2,711	2,811	2,568
Other income (expense), net	36	62	50
Defined Benefit Plan, Other Cost (Credit)	253	258	256
Interest expense
Interest expense	1,142	1,198	1,243
Net income (loss)	1,352	1,417	1,119
ALABAMA
Operating revenues
Electric revenue	1,439	1,593	1,600
GEORGIA
Operating revenues
Electric revenue	249	270	267
KENTUCKY
Operating revenues
Electric revenue	624	691	696
MISSISSIPPI
Operating revenues
Electric revenue	941	1,063	1,052
NORTH CAROLINA
Operating revenues
Electric revenue	65	74	66
TENNESSEE
Operating revenues
Electric revenue	6,740	7,419	7,350
VIRGINIA
Operating revenues
Electric revenue	$ 42	$ 45	$ 48

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Current assets
Cash and Cash Equivalents, at Carrying Value	$ 500	$ 299
Accounts receivable, net	1,529	1,739
Inventories, net	1,003	999
Regulatory assets	130	156
Other current assets	84	85
Total current assets	3,246	3,278
Property, plant, and equipment
Completed plant	64,970	62,944
Less accumulated depreciation	(33,550)	(31,384)
Net completed plant	31,420	31,560
Construction in progress	2,139	1,893
Nuclear fuel	1,504	1,534
Capital leases	516	146
Total property, plant, and equipment, net	35,579	35,133
Long-term Investments	3,198	2,968
Regulatory and other long-term assets
Regulatory assets	10,245	8,763
Operating Lease, Right-of-Use Asset	232	0
Other long-term assets	325	325
Total regulatory and other long-term assets	10,802	9,088
Total assets	52,825	50,467
Current liabilities
Accounts payable and accrued liabilities	1,844	1,649
Accrued interest	298	296
Asset Retirement Obligation, Current	345	163
Current portion of leaseback obligations	198	40
Regulatory liabilities	141	150
Short-term debt, net of discounts	57	922
Total Current maturities of power bonds issued at par	1,787	1,030
Current maturities of long-term debt of variable interest entities issued at par	41	39
Current maturities of notes payable	0	23
Total current liabilities	4,711	4,312
Other liabilities
Post-retirement and post-employment benefit obligations	6,617	6,181
Asset retirement obligations	6,440	5,453
Finance Lease, Liability	525	182
Other long-term liabilities	2,548	2,308
Leaseback obligations	25	223
Non-current regulatory liabilities	23	0
Total other liabilities	16,178	14,347
Long-term debt, net
Long-term power bonds, net	17,956	19,094
Long-term debt of variable interest entities, net	1,048	1,089
Total long-term debt, net	19,004	20,183
Total liabilities	39,893	38,842
Proprietary capital
Power program appropriation investment	258	258
Power program retained earnings	12,177	10,823
Total power program proprietary capital	12,435	11,081
Nonpower programs appropriation investment, net	548	556
Accumulated other comprehensive income (loss)	(51)	(12)
Total proprietary capital	12,932	11,625
Total liabilities and proprietary capital	$ 52,825	$ 50,467

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Regulatory asset amount expensed	$ (23)	$ (261)	$ (2)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	521	322	322
Cash flows from operating activities
Net income (loss)	1,352	1,417	1,119
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)	1,848	1,993	2,554
Amortization of nuclear fuel cost	388	379	382
Non-cash retirement benefit expense	324	314	324
Prepayment credits applied to revenue	0	(10)	(100)
Changes in current assets and liabilities
Accounts receivable, net	259	(40)	(68)
Inventories and other current assets, net	(12)	(87)	65
Accounts payable and accrued liabilities	(38)	(155)	143
Accrued interest	1	(8)	(36)
Pension contributions	(305)	(307)	(304)
Settlements of asset retirement obligations	(114)	(89)	(106)
Other, net	(44)	52	(37)
Net cash provided by operating activities	3,636	3,720	3,938
Cash flows from investing activities
Construction expenditures	(1,643)	(1,700)	(1,759)
Nuclear fuel expenditures	(342)	(474)	(457)
Purchases of investments	(49)	(48)	(49)
Loans and other receivables
Advances	(8)	(10)	(12)
Repayments	7	11	4
Other, net	20	(22)	4
Net cash used in investing activities	(2,015)	(2,243)	(2,269)
Long-term debt
Issues of power bonds	997	0	998
Redemptions and repurchases of power bonds	(1,427)	(1,035)	(1,731)
Redemptions of notes payable	(23)	(46)	(53)
Payments on debt of variable interest entities	(39)	(38)	(36)
Short-term debt issues (redemptions), net	(865)	(294)	(782)
Payments on leases and leasebacks	(55)	(43)	(42)
Financing costs, net	(4)	0	(3)
Other, net	(6)	(21)	(9)
Net cash (used in) provided by financing activities	(1,422)	(1,477)	(1,658)
Net change in cash and cash equivalents	199	0	$ 11
Cash and cash equivalents at beginning of the year	299
Cash and cash equivalents at end of the year	$ 500	$ 299

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN PROPRIETARY CAPITAL - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Balance at beginning of year		$ 11,625		$ 10,283	$ 11,625	$ 10,283	$ 9,133
Net income (loss)	$ 700	192	$ 588	423	1,352	1,417	1,119
Total other comprehensive income (loss)					(39)	(69)	36
Return on power program appropriation investment					(6)	(6)	(5)
Balance at end of year	12,932		11,625		12,932	11,625	10,283
Power Program Appropriation Investment
Balance at beginning of year		258		258	258	258	258
Net income (loss)					0	0	0
Total other comprehensive income (loss)					0	0	0
Return on power program appropriation investment					0	0	0
Balance at end of year	258		258		258	258	258
Power Program Retained Earnings
Balance at beginning of year		10,823		9,404	10,823	9,404	8,282
Net income (loss)					1,360	1,425	1,127
Total other comprehensive income (loss)					0	0	0
Return on power program appropriation investment					(6)	(6)	(5)
Balance at end of year	12,177		10,823		12,177	10,823	9,404
Nonpower Programs Appropriation Investment, Net
Balance at beginning of year		556		564	556	564	572
Net income (loss)					(8)	(8)	(8)
Total other comprehensive income (loss)					0	0	0
Return on power program appropriation investment					0	0	0
Balance at end of year	548		556		548	556	564
Accumulated Other Comprehensive Income (Loss) Net Gains (Losses) on Cash Flow Hedges
Balance at beginning of year		$ (12)		$ 57	(12)	57	21
Net income (loss)					0	0	0
Total other comprehensive income (loss)					(39)	(69)	36
Return on power program appropriation investment					0	0	0
Balance at end of year	$ (51)		$ (12)		$ (51)	$ (12)	$ 57

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) Statement - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 1,352	$ 1,417	$ 1,119
Net unrealized gain (loss) on cash flow hedges	(1)	(114)	10
Reclassification to earnings from cash flow hedges	(38)	(45)	(26)
Total other comprehensive income (loss)	(39)	(69)	36
Total comprehensive income (loss)	$ 1,313	$ 1,348	$ 1,155

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information Interest paid was $1.1 billion for 2020 and $1.2 billion for both 2019 and 2018. These amounts differ from interest expense in certain years due to the timing of payments. There was no interest capitalized in 2020, 2019, or 2018. Construction in progress and Nuclear fuel expenditures included in Accounts payable and accrued liabilities at September 30, 2020, 2019, and 2018 were $398 million, $324 million, and $372 million, respectively, and are excluded from the Statements of Consolidated Cash Flows for the years ended September 30, 2020, 2019, and 2018 as non-cash investing activities. Excluded from the Statements of Consolidated Cash Flows for the years ended September 30, 2020 and 2019, as non-cash financing activities were $394 million related to lease obligations incurred primarily in connection with a PPA and $10 million related to lease obligations incurred for leased equipment, respectively. There were no capital leases incurred during 2018. See Note 7 — Leases for further information regarding TVA's finance leases. Also excluded from the Statement of Consolidated Cash Flows for the year ended September 30, 2020, were $80 million and $73 million as non-cash financing and investing activities, respectively, due to derecognition of the Paradise pipeline financing obligation and asset. Cash flows from swap contracts that are accounted for as hedges are classified in the same category as the item being hedged or on a basis consistent with the nature of the instrument.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Supplemental Cash Flow Information
Interest paid	$ 1,100	$ 1,200
Capital lease obligations incurred	394	10
Non-cash financing activities	80
Non-cash investing activities	73
Interest Paid, Excluding Capitalized Interest, Operating Activities	1,100	1,200
Accounts payable and accrued liabilities
Supplemental Cash Flow Information
Construction in progress and Nuclear fuel expenditures	$ 398	$ 324	$ 372

Summary of Significant Accounti

Summary of Significant Accounting Policies [Text Block]	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
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 approximately 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 United States 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 power 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 power 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 other 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 The accompanying consolidated 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 10 — 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, including impacts from the COVID-19 pandemic, 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 Consolidated Balance Sheet at September 30, 2019, TVA reclassified $163 million from Accounts payable and accrued liabilities to Asset retirement obligations in Current liabilities. In addition, as a result of the adoption of the new lease accounting standard effective for TVA October 1, 2019, TVA reclassified $182 million from Other long-term liabilities to Finance lease liabilities in the Consolidated Balance Sheet at September 30, 2019. 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 22 — Commitments and Contingencies — Legal Proceedings — Environmental Agreements . The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported in the Consolidated Balance Sheets and Consolidated Statements of Cash Flows: Cash, Cash Equivalents, and Restricted Cash 2020 2019 Cash and cash equivalents $ 500 $ 299 Restricted cash and cash equivalents, included in Other long-term assets 21 23 Total Cash, cash equivalents, and restricted cash $ 521 $ 322 Due to higher volatility in the financial markets associated with the COVID-19 pandemic, TVA increased its target balance of Cash and cash equivalents beginning in March 2020. TVA continued to hold higher target cash balances at September 30, 2020, and may hold higher balances in future periods due to potential market volatility. 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. TVA continues to monitor the impact of the COVID-19 pandemic on accounts and loans receivable balances to evaluate the allowance for uncollectible accounts. The allowance for uncollectible accounts was less than $1 million at both September 30, 2020 and 2019, for accounts receivable. Additionally, loans receivable of $105 million and $131 million at September 30, 2020 and 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 September 30, 2020 and 2019, respectively. 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. Pre-Commercial Plant Operations As part of the process of completing the construction of a generating unit, the electricity produced is used to serve the demands of the electric system. TVA estimates revenue from such pre-commercial generation based on the guidance provided by Federal Energy Regulatory Commission ("FERC") regulations. The Allen Combined Cycle Plant ("Allen CC") began pre-commercial plant operations in September 2017, and began commercial operations in April 2018. Cogeneration capability at Johnsonville Combustion Turbine Unit 20 commenced pre-commercial plant operations in September 2017, and was placed in service during December 2017. Estimated revenue of $11 million related to Allen CC was capitalized to offset project costs for the year ended September 30, 2018. TVA also capitalized related fuel costs for these construction projects of approximately $19 million during the year ended September 30, 2018. No such amounts were capitalized during 2019 or 2020. Inventories Certain Fuel, Materials, and Supplies . Materials and supplies inventories are valued using an average unit cost method. A new average cost is computed after each inventory purchase transaction, and inventory issuances are priced at the latest moving weighted average unit cost. Coal, fuel oil, and natural gas inventories are valued using an average cost method. A new weighted average cost is computed monthly, and monthly issues are priced accordingly. Renewable Energy Credits. TVA accounts for Renewable Energy Certificates ("RECs") using the specific identification cost method. RECs that are acquired through power purchases are recorded as inventory and charged to purchased power expense when the RECs are subsequently used or sold. TVA assigns a value to the RECs at the inception of the power purchase arrangement using a relative fair value approach. RECs created through TVA-owned asset generation are recorded at zero cost. Emission Allowances . TVA has emission allowances for sulfur dioxide ("SO 2 ") and nitrogen oxide ("NO x ") which are accounted for as inventory. The cost of specific allowances used each month is charged to operating expense based on tons of SO 2 and NO x emitted during the respective compliance periods. Allowances granted to TVA by the Environmental Protection Agency ("EPA") are recorded at zero cost. Allowance for Inventory Obsolescence . TVA reviews materials and supplies inventories by category and usage on a periodic basis. Each category is assigned a probability of becoming obsolete based on the type of material and historical usage data. In 2018, TVA started moving from a site-specific inventory management policy to a fleet-wide strategy for each generation type. Based on the estimated value of the inventory, TVA adjusts its allowance for inventory obsolescence. Property, Plant, and Equipment, and Depreciation Property, Plant, and Equipment. Additions to plant are recorded at cost, which includes direct and indirect costs. The cost of current repairs and minor replacements is charged to operating expense. Nuclear fuel, which is included in Property, plant, and equipment, is valued using the average cost method for raw materials and the specific identification method for nuclear fuel in a reactor. Amortization of nuclear fuel in a reactor is calculated on a units-of-production basis and is included in fuel expense. When property, plant, and equipment is retired, accumulated depreciation is charged for the original cost of the assets. Gains or losses are only recognized upon the sale of land or an entire operating unit. 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 will be updated approximately every five years. Depreciation expense for the years ended September 30, 2020, 2019, and 2018 was $1.6 billion, $1.8 billion, and $1.3 billion, respectively. Depreciation expense expressed as a percentage of the average annual depreciable completed plant was 2.74 percent for 2020, 3.09 percent for 2019, and 2.45 percent for 2018. Average depreciation rates by asset class are as follows: Property, Plant, and Equipment Depreciation Rates At September 30 2020 2019 2018 Asset Class Nuclear 2.38 2.38 2.64 Coal-fired (1) 3.62 4.96 2.32 Hydroelectric 1.60 1.61 1.57 Gas and oil-fired 3.04 3.00 2.93 Transmission 1.34 1.34 1.32 Other 7.26 7.16 5.90 Note (1) The rates include the acceleration of depreciation related to retiring certain coal-fired units. Coal-Fired . As a result of TVA's decision to idle or retire certain units since the previous depreciation study, TVA recognized $387 million, $566 million, and $48 million in accelerated depreciation expense related to the units during the years ended September 30, 2020, 2019, and 2018, respectively. Accelerated depreciation is based on the remaining useful life of the asset at the time the decision is made to idle or retire a unit. Reacquired Rights . Property, plant, and equipment includes intangible reacquired rights, net of amortization, of $192 million and $200 million as of September 30, 2020 and 2019, respectively, related to the purchase of residual interests from lease/leaseback agreements of certain combustion turbine units ("CTs"). Reacquired rights are amortized over the estimated useful life of the underlying CTs. Amortization expense was $8 million for all years 2020, 2019, and 2018. Software Costs. TVA capitalizes certain costs incurred in connection with developing or obtaining internal-use software. Capitalized software costs are included in Property, plant, and equipment on the Consolidated Balance Sheets and are generally amortized over seven years. At September 30, 2020 and 2019, unamortized computer software costs totaled $54 million and $63 million, respectively. Amortization expense related to capitalized computer software costs was $42 million, $38 million, and $32 million for 2020, 2019, and 2018, respectively. Software costs that do not meet capitalization criteria are expensed as incurred. Impairment of Assets. TVA evaluates long-lived assets for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. For long-lived assets, TVA bases its evaluation on impairment indicators such as the nature of the assets, the future economic benefit of the assets, any historical or future profitability measurements, regulatory approval and ability to set rates at levels that allow for recoverability of the assets, and other external market conditions or factors that may be present. If such impairment indicators are present or other factors exist that indicate that the carrying amount of an asset may not be recoverable, TVA determines whether an impairment has occurred based on an estimate of undiscounted cash flows attributable to the asset as compared with the carrying value of the asset. If an impairment has occurred, the amount of the impairment recognized is measured as the excess of the asset's carrying value over its fair value. Additionally, TVA regularly evaluates construction projects. If the project is canceled or deemed to have no future economic benefit, the project is written off as an asset impairment or, upon TVA Board approval, reclassified as a regulatory asset. See Note 6 — Plant Closures . 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 ("PPAs") 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 power purchase agreements, the terms of which vary. The total lease obligation included in Accounts payable and accrued liabilities and lease liabilities related to these agreements were $500 million and $174 million for finance and operating leases, respectively, at September 30, 2020. 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 September 30, 2020. 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. Decommissioning Costs TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets. These obligations relate to fossil fuel-fired generating plants, nuclear generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. These other property-related assets include, but are not limited to, easements and coal rights. Activities involved with retiring these assets could include decontamination and demolition of structures, removal and disposal of wastes, and site restoration. Revisions to the estimates of asset retirement obligations ("AROs") are made whenever factors indicate that the timing or amounts of estimated cash flows have changed materially. Any accretion or depreciation expense related to these liabilities and assets is charged to a regulatory asset. See Note 9 — Regulatory Assets and Liabilities — Nuclear Decommissioning Costs and Non-Nuclear Decommissioning Costs and Note 12 — Asset Retirement Obligations. Down-blend Offering for Tritium TVA, the Department of Energy ("DOE"), and certain nuclear fuel contractors have entered into agreements, referred to as the Down-blend Offering for Tritium, that provide for the production, processing, and storage of low-enriched uranium that is to be made using surplus DOE highly enriched uranium and other uranium. Low-enriched uranium can be fabricated into fuel for use in a nuclear power plant. Production of the low-enriched uranium began in 2019 and is contracted to continue through October 2027. Beginning October 2027, contract activity will consist of storage and flag management. Flag management ensures that the uranium is of U.S. origin, free from foreign obligations, and unencumbered by policy restrictions, so that it can be used in connection with the production of tritium. Under the terms of the interagency agreement between the DOE and TVA, the DOE will reimburse TVA for a portion of the costs of converting the highly enriched uranium to low-enriched uranium. Since 2019, TVA has received $89 million in reimbursements from the DOE. At September 30, 2020, TVA recorded $6 million in Accounts receivable, net related to this agreement. Investment Funds Investment funds consist primarily of trust funds designated to fund decommissioning requirements (see Note 22 — Commitments and Contingencies — Decommissioning Costs ), the Supplemental Executive Retirement Plan ("SERP") (see Note 21 — Benefit Plans — Overview of Plans and Benefits — Supplemental Executive Retirement Plan ), and the Deferred Compensation Plan ("DCP"). The Nuclear Decommissioning Trust ("NDT") holds funds primarily for the ultimate decommissioning of TVA's nuclear power plants. The Asset Retirement Trust ("ART") holds funds primarily for the costs related to the future closure and retirement of TVA's other long-lived assets. 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 funds are all classified as trading. Energy Prepayment Obligations In 2004, TVA and its largest customer, Memphis Light, Gas and Water Division ("MLGW"), entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 180 months. TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations. The arrangement ceased in 2019. Revenue was recognized in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as non-cash revenue on a cumulative basis during the life of the agreement, $10 million and $100 million of which was recognized as non-cash revenue during 2019 and 2018, respectively. Discounts to account for the time value of money, which are recorded as a reduction to electricity sales, amounted to $4 million and $46 million for the years ended September 30, 2019 and 2018, respectively. Insurance Although TVA uses private companies to administer its healthcare plans for eligible active and retired employees not covered by Medicare, TVA does not purchase health insurance. Third-party actuarial specialists assist TVA in determining certain liabilities for self-insured claims. TVA recovers the costs of claims through power rates and through adjustments to the participants' contributions to their benefit plans. These liabilities are included in Other liabilities on the Consolidated Balance Sheets. TVA sponsors an Owner Controlled Insurance Program which provides workers' compensation and liability insurance for a select group of contractors performing maintenance, modifications, outage, and new construction activities at TVA facilities. The Federal Employees' Compensation Act ("FECA") governs liability to employees for service-connected injuries. TVA purchases excess workers' compensation insurance above a self-insured retention. In addition to excess workers' compensation insurance, TVA purchases the following types of insurance: • Nuclear liability insurance; nuclear property, decommissioning, and decontamination insurance; and nuclear accidental outage insurance. See Note 22 — Commitments and Contingencies — Nuclear Insurance . • Excess liability insurance for aviation, auto, marine, and general liability exposures. • Property insurance for certain conventional (non-nuclear) assets. The insurance policies are subject to the terms and conditions of the specific policy, including deductibles or self-insured retentions. To the extent insurance would not provide either a partial or total recovery of the costs associated with a loss, TVA would have to recover any such costs through other means, including through power rates. Research and Development Costs Research and development costs are expensed when incurred. TVA's research programs include those related to power delivery technologies, emerging technologies (clean energy, renewables, distributed resources, and energy efficiency), technologies related to generation (fossil fuel, nuclear, and hydroelectric), and environmental technologies. Tax Equivalents TVA is not subject to federal income taxation. In addition, neither TVA nor its property, franchises, or income is subject to taxation by states or their subdivisions. The TVA Act requires TVA to make payments to states and counties in which TVA conducts its power operations and in which TVA has acquired power properties previously subject to state and local taxation. The total amount of these payments is five percent of gross revenues from sales of power during the preceding year, excluding sales or deliveries to other federal agencies and off-system sales with other utilities, with a provision for minimum payments under certain circumstances. TVA calculates tax equivalent expense by subtracting the prior year fuel cost-related tax equivalent regulatory asset or liability from the payments made to the states and counties during the current year and adding back the current year fuel cost-related tax equivalent regulatory asset or liability. Fuel cost-related tax equivalent expense is recognized in the same accounting period in which the fuel cost-related revenue is recognized. Maintenance Costs

Impact of New Accounting Standa

Impact of New Accounting Standards and Interpretations	12 Months Ended
	Sep. 30, 2020
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Update and Change in Accounting Principle [Text Block]	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. Effective Date for TVA October 1, 2019 Effect on the Financial Statements or Other Significant Matters TVA 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 (1) apply transition requirements at adoption date, (2) recognize cumulative effect adjustment to retained earnings in period of adoption, and (3) 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 had 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 TVA has adopted the standard on a prospective basis. Adoption of this standard did not have a material impact on TVA's financial condition, results of operations, 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 as of September 30, 2020, 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. Effect on the Financial Statements or Other Significant Matters TVA adopted this standard using the modified retrospective method through a cumulative-effect adjustment to retained earnings on October 1, 2020. TVA will recognize an allowance that reflects the current estimate of credit losses expected to be incurred over the life of the financial assets based on historical experience, current conditions, and reasonable and supportable forecasts. This standard will primarily impact TVA's long-term loans receivable. Adoption of this standard is not expected to have a material impact on TVA's financial condition, results of operations, or cash flows. 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. 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. Reference Rate Reform Description The guidance provides temporary optional expedients and exceptions to the guidance in GAAP on contract modifications and hedge accounting to ease the financial reporting burdens related to the expected market transition from the London Interbank Offered Rate ("LIBOR") and other interbank offered rates to alternative reference rates, such as the Secured Overnight Financing Rates. Effective Date for TVA The new standard is effective for adoption at any time between March 12, 2020, and December 31, 2022. TVA currently plans to adopt the standard by December 31, 2022. Effect on the Financial Statements or Other Significant Matters TVA continues to review this standard and evaluate the impact of using an alternative reference rate instead of LIBOR in its interest rate swap contracts. TVA expects the adoption of the standard will simplify the accounting for any modifications to its interest rate swap contracts.

Accounts Receivable, Net

Accounts Receivable, Net	12 Months Ended
	Sep. 30, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Accounts Receivable, Net	3. 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 September 30 2020 2019 Power receivables $ 1,401 $ 1,624 Other receivables 128 115 Accounts receivable, net (1) $ 1,529 $ 1,739 Note (1) Allowance for uncollectible accounts was less than $1 million at September 30, 2020 and 2019, and therefore is not represented in the table above.

Inventories, Net

Inventories, Net	12 Months Ended
	Sep. 30, 2020
Inventory, Net [Abstract]
Inventories, Net	4. Inventories, Net The table below summarizes the types and amounts of TVA's inventories: Inventories, Net At September 30 2020 2019 Materials and supplies inventory $ 770 $ 742 Fuel inventory 253 294 RECs inventory, net 15 16 Allowance for inventory obsolescence (35) (53) Inventories, net $ 1,003 $ 999

Net Completed Plant

Net Completed Plant	12 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant, and Equipment and Intangible Assets	Net Completed Plant Net completed plant consisted of the following: Net Completed Plant At September 30 2020 2019 Cost Accumulated Depreciation Cost Accumulated Depreciation Net Coal-fired (1)(2) $ 18,613 $ 13,944 $ 4,669 $ 17,400 $ 12,538 $ 4,862 Gas and oil-fired 6,010 1,696 4,314 6,054 1,562 4,492 Nuclear 25,741 12,141 13,600 25,543 11,656 13,887 Transmission 8,283 3,140 5,143 7,932 3,083 4,849 Hydroelectric 3,410 1,090 2,320 3,163 1,051 2,112 Other electrical plant 1,981 1,146 835 1,920 1,110 810 Intangible software 3 2 1 3 1 2 Multipurpose dams 900 381 519 900 373 527 Other stewardship 29 10 19 29 10 19 Total $ 64,970 $ 33,550 $ 31,420 $ 62,944 $ 31,384 $ 31,560 Notes (1) TVA recognized accelerated depreciation as a result of the decision to idle or retire certain units. See Note 6 — Plant Closures . (2) In 2020, TVA recorded approximately $1.1 billion in upward revisions to asset retirement costs for coal-fired assets. See Note 12 — Asset Retirement Obligations .

Other Long-Term Assets _Text Bl

Other Long-Term Assets [Text Block]	12 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Long-Term Assets	8. Other Long-Term Assets The table below summarizes the types and amounts of TVA's other long-term assets: Other Long-Term Assets At September 30 2020 2019 (1) Loans and other long-term receivables, net $ 100 $ 125 EnergyRight ® receivables 69 81 Prepaid long-term service agreements 42 22 Commodity contract derivative assets 23 — Restricted cash and cash equivalents 21 23 Prepaid capacity payments 11 19 Other 59 55 Total other long-term assets $ 325 $ 325 Note (1) At September 30, 2019, $22 million previously classified as Other (a component of Other long-term assets) has been reclassified to Prepaid long-term service agreements (a component of Other long-term assets) to conform with current year presentation. EnergyRight ® Receivables . In association with the EnergyRight ® 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 September 30, 2020 and 2019, the carrying amount of the loans receivable, net of discount, reported in Accounts receivable, net was approximately $18 million and $20 million, respectively. See Note 11 — Other Long-Term Liabilities for information regarding the associated financing obligation. In response to the COVID-19 pandemic, customers experiencing financial hardship can request a deferral of EnergyRight ® loan payments for a period of up to six months. This deferral option began April 20, 2020, and is available through October 31, 2020. Deferred loans will not accrue interest during the deferral months. These deferred loans have resulted in a less than $1 million impact to TVA. 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 September 30, 2020 and 2019, prepayments of $3 million and $5 million, respectively, were recorded in Other current assets.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities [Text Block]	12 Months Ended
	Sep. 30, 2020
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 At September 30 2020 2019 (1) Current regulatory assets Unrealized losses on interest rate derivatives $ 114 $ 89 Unrealized losses on commodity derivatives 4 39 Fuel cost adjustment receivable 12 28 Total current regulatory assets 130 156 Non-current regulatory assets Deferred pension costs and other post-retirement benefits costs 5,193 4,756 Non-nuclear decommissioning costs 2,512 1,741 Unrealized losses on interest rate derivatives 1,506 1,241 Nuclear decommissioning costs 896 868 Unrealized losses on commodity derivatives — 15 Other non-current regulatory assets 138 142 Total non-current regulatory assets 10,245 8,763 Total regulatory assets $ 10,375 $ 8,919 Current regulatory liabilities Fuel cost adjustment tax equivalents $ 115 $ 138 Unrealized gains on commodity derivatives 26 12 Total current regulatory liabilities 141 150 Non-current regulatory liabilities Unrealized gains on commodity derivatives 23 — Total non-current regulatory liabilities 23 — Total regulatory liabilities $ 164 $ 150 Note (1) At September 30, 2019, $12 million previously classified as Environmental agreements (a component of Regulatory assets) has been reclassified to Other non-current regulatory assets (a component of Regulatory assets) to conform with current year presentation. In 2017, the TVA Board authorized management to accelerate amortization of certain regulatory assets to the extent actual net income in 2018 exceeded the budgeted amount, up to the aggregate amount of those certain regulatory assets. Assets included in this TVA Board action include: deferred nuclear generating units, environmental cleanup costs related to the Kingston ash spill, and nuclear training costs related to the refurbishing and restarting of Browns Ferry Nuclear Plant ("Browns Ferry") Unit 1 and the construction of Watts Bar Nuclear Plant ("Watts Bar") Unit 2. TVA recorded $857 million of accelerated amortization of the Deferred nuclear generating units and Nuclear training costs regulatory assets in 2018. The TVA Board authorized TVA to use the amount included in the 2019 rate action for these two regulatory assets, to the extent needed, to accelerate amortization of the Environmental cleanup costs - Kingston ash spill regulatory asset in 2019. TVA recorded $266 million of accelerated recovery for the Kingston ash spill regulatory asset in 2019. No accelerated amortization was recorded in 2020. Deferred Pension Costs and Other Post-retirement Benefit Costs . TVA measures the funded status of its pension and post-retirement ("OPEB") benefit plans at each year-end balance sheet date. The funded status is measured as the difference between the fair value of plan assets and the benefit obligations at the measurement date for each plan. The changes in funded status are actuarial gains and losses that are recognized on TVA's Consolidated Balance Sheets by adjusting the recognized pension and OPEB liabilities, with the offset deferred as a regulatory asset or a regulatory liability. In an unregulated environment, these deferred costs would be recognized as an increase or decrease to accumulated other comprehensive income (loss) ("AOCI"). "Incurred cost" is a cost arising from cash paid out or an obligation to pay for an acquired asset or service, and a loss from any cause that has been sustained and for which payment has been or must be made. In the cases of pension and OPEB costs, the unfunded obligation represents a projected liability to the employee for services rendered, and thus it meets the definition of an incurred cost. Therefore, amounts that otherwise would be charged to AOCI for these costs are recorded as a regulatory asset or liability since TVA has historically recovered pension and OPEB expense in rates. Through historical and current year expense included in ratemaking, the TVA Board has demonstrated the ability and intent to include pension and OPEB costs in allowable costs and in rates for ratemaking purposes. As a result, it is probable that future revenue will result from inclusion of the pension and OPEB regulatory assets or regulatory liability in allowable costs for ratemaking purposes. The regulatory asset and liability are classified as long-term, which is consistent with the pension and OPEB liabilities, and are not amortized to the consolidated statements of operations over a specified recovery period. They are adjusted either upward or downward each year in conjunction with the adjustments to the unfunded pension liability and OPEB liability, as calculated by the actuaries. Ultimately the regulatory asset and liability will be recognized in the consolidated statements of operations in the form of pension and OPEB expense as the actuarial liabilities are eliminated in future periods. See Note 21 — Benefit Plans — Obligations and Funded Status . Additionally on October 1, 2014, TVA began recognizing pension costs as a regulatory asset to the extent that the amount calculated under GAAP as pension expense differs from the amount TVA contributes to the pension plan. As a result of recent plan design changes, future contributions are expected to exceed the expense calculated under U.S. GAAP. Accordingly, TVA will discontinue this regulatory accounting practice once all such deferred costs have been recovered, at which time it will recognize pension costs in accordance with U.S. GAAP. Non-Nuclear Decommissioning Costs. Non-nuclear decommissioning costs include: (1) certain deferred charges related to the future closure and decommissioning of TVA's non-nuclear long-lived assets, (2) recognition of changes in the liability, (3) recognition of changes in the value of TVA's ART, and (4) certain other deferred charges under the accounting rules for AROs. TVA has established the ART to more effectively segregate, manage, and invest funds to help meet future non-nuclear AROs. The funds from the ART may be used, among other things, to pay the costs related to the future closure and retirement of non-nuclear long-lived assets under various legal requirements. These future costs can be funded through a combination of investment funds already set aside in the ART, future earnings on those investment funds, and future cash contributions to the ART and future earnings thereon. For 2020, TVA recovered in rates a portion of its estimated current year non-nuclear decommissioning costs and contributions to the ART. Deferred charges will be recovered in rates based on an analysis of the expected expenditures, contributions, and investment earnings required to recover the decommissioning costs. There is not a specified recovery period; therefore, the regulatory asset is classified as long-term consistent with the ART investments and ARO liability. Unrealized Losses on Interest Rate Derivatives . TVA uses regulatory accounting treatment to defer the unrealized gains and losses on certain interest rate derivative contracts. When amounts in these contracts are realized, the resulting gains or losses are included in the ratemaking formula. The unrealized losses on these interest rate derivatives are recorded on TVA's Consolidated Balance Sheets as current and non-current regulatory assets, and the related realized gains or losses, if any, are recorded on TVA's Consolidated Statements of Operations when the contracts settle. A portion of certain unrealized gains and losses will be amortized into earnings over the remaining lives of the contracts. Gains and losses on interest rate derivatives that are expected to be realized within the next year are included as a current regulatory asset or liability on TVA's Consolidated Balance Sheet. Due to changing interest rates in the financial markets associated with the COVID-19 pandemic, TVA has experienced unrealized losses related to its derivative instruments for the year ended September 30, 2020. TVA does not recognize unrealized gains and losses from the investment portfolios and derivative instruments within earnings but rather defers all such gains and losses within a regulatory liability or asset in accordance with its accounting policy. See Note 15 — Risk Management Activities and Derivative Transactions and Note 16 — Fair Value Measurements. Nuclear Decommissioning Costs. Nuclear decommissioning costs include: (1) certain deferred charges related to the future closure and decommissioning of TVA's nuclear generating units under the Nuclear Regulatory Commission ("NRC") requirements, (2) recognition of changes in the liability, (3) recognition of changes in the value of TVA's NDT, and (4) certain other deferred charges under the accounting rules for AROs. These future costs can be funded through a combination of investment funds set aside in the NDT and ART, future earnings on the investment funds, and future earnings thereon. Deferred charges will be recovered in rates based on the analysis of expected expenditures, contributions, and investment earnings required to recover the decommissioning costs. See Note 1 — Summary of Significant Accounting Policies — Investment Funds. There is not a specified recovery period; therefore, the regulatory asset is classified as long-term consistent with the NDT investments and ARO liability. Unrealized Gains (Losses) on Commodity Derivatives. Unrealized gains (losses) on natural gas purchase contracts, included as part of unrealized gains (losses) on commodity derivatives, relate to the mark-to-market ("MtM") valuation of natural gas purchase contracts. During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts because these contracts no longer meet the criteria of net settlement. As a result, the associated net regulatory assets have been derecognized. The natural gas purchase contracts qualify as derivative contracts but do not qualify for cash flow hedge accounting treatment. As a result, TVA recognizes the changes in the market value of these derivative contracts as a regulatory liability or asset. This treatment reflects TVA's ability and intent to recover the cost of these commodity contracts on a settlement basis for ratemaking purposes through the fuel cost adjustment. TVA recognizes the actual cost of fuel received under these contracts in fuel expense at the time the fuel is used to generate electricity. These contracts expire at various times through 2024. Unrealized gains and losses on contracts with a maturity of less than one year are included as a current regulatory asset or liability on TVA's Consolidated Balance Sheets. See Note 15 — Risk Management Activities and Derivative Transactions . Fuel Cost Adjustment Receivable. The fuel cost adjustment provides a mechanism to alter rates monthly to reflect changing fuel and purchased power costs. There is typically a lag between the occurrence of a change in fuel and purchased power costs and the reflection of the change in fuel rates. Balances in the fuel cost adjustment regulatory accounts represent over-collected or under-collected revenues that offset fuel and purchased power costs, and the fuel rate is designed to recover or refund the balance in less than one year. Other Non-Current Regulatory Assets. Other non-current regulatory assets consist of the following: Deferred Capital Leases and Other Financing Obligations . For certain leases that were determined prior to TVA's adoption of the new lease accounting standard effective October 1, 2019, TVA recognized the initial capital lease liability and asset at inception. However, the annual expense recognized in rates is equal to the annual lease payments, which differs from GAAP treatment. This practice results in TVA's asset balances being higher than they otherwise would have been under GAAP, with the difference representing a regulatory asset related to each capital lease. These costs will be amortized over the respective lease as lease payments are made. As the costs associated with this regulatory asset are not currently being considered in rates and the asset is expected to increase over the next year, the regulatory asset has been classified as long-term. Debt Reacquisition Costs . Reacquisition expenses, call premiums, and other related costs, such as unamortized debt issue costs associated with redeemed Bond issues, are deferred and amortized (accreted) on a straight-line basis over the weighted average life of TVA's debt portfolio. Because timing of additional reacquisition expenses and changes to the weighted average life of the debt are uncertain, the regulatory asset is classified as long-term. Retirement Removal Costs . Retirement removal costs, net of salvage, that are not legally required are recognized as a regulatory asset. Net removal costs are amortized over a one-year period subsequent to completion of the removal activities. TVA treats this regulatory asset as long-term in its entirety primarily because it relates to assets that are long-term in nature.

Asset Acquisitions and Business

Asset Acquisitions and Business Combinations (Notes)	12 Months Ended
	Sep. 30, 2020
Business Combinations and Settlement of Preexisting Relationships [Abstract]
Asset Acquisitions and Business Combinations Disclosure	Asset Acquisitions On September 20, 2017, TVA acquired 100 percent of the equity interests in two special purpose entities ("SPEs") designed to administer rent payments TVA makes under certain of its lease/leaseback arrangements. Each entity holds residual interests in four of TVA's peaking combustion turbine units ("CTs"). TVA acquired these entities in order to reacquire the residual interests in eight CTs it had previously granted in the lease/leaseback arrangements. TVA acquired the entities for total cash consideration of $36 million. The fair value of the assets acquired consisted of $110 million of reacquired rights, and the fair value of liabilities assumed consisted of $74 million in notes payable. Reacquired rights are an intangible asset included in TVA's Completed plant balance and are amortized over the estimated useful life of the underlying CTs. Notes payable assumed in the transaction were paid in full during 2020. TVA recognized less than $1 million of amortization expense, related to reacquired rights, within TVA's consolidated statements of operations. Transaction costs were not material. TVA determined that its lease/leaseback obligations were preexisting relationships that were effectively settled in the asset acquisitions. TVA settled the preexisting relationships separately from the asset acquisitions, resulting in a loss on extinguishment of the obligations of $3 million. The carrying value of lease/leaseback obligations effectively settled was $71 million, including accrued interest, and the reacquisition price was $74 million, paid in cash, at the acquisition date.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	10. 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 in 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 as of September 30, 2020 and 2019, as reflected on the Consolidated Balance Sheets, are as follows: Summary of Impact of VIEs on Consolidated Balance Sheets At September 30 2020 2019 Current liabilities Accrued interest $ 10 $ 11 Accounts payable and accrued liabilities 3 3 Current maturities of long-term debt of variable interest entities 41 39 Total current liabilities 54 53 Other liabilities Other long-term liabilities 23 25 Long-term debt, net Long-term debt of variable interest entities, net 1,048 1,089 Total liabilities $ 1,125 $ 1,167 Interest expense of $54 million, $56 million, and $58 million related to debt of VIEs and membership interests of variable interest entity subject to mandatory redemption is included in the Consolidated Statements of Operations for the years ended September 30, 2020, 2019, and 2018, respectively. Creditors of the VIEs do not have any 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	12 Months Ended
	Sep. 30, 2020
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 as well as for environmental remediation liabilities and liabilities under agreements related to compliance with certain environmental regulations. See Note 12 — Asset Retirement Obligations , Note 15 — Risk Management Activities and Derivative Transactions — Derivatives Not Receiving Hedge Accounting Treatment — Interest Rate Derivatives , and Note 22 — Commitments and Contingencies — Legal Proceedings — Environmental Agreements . The table below summarizes the types and amounts of Other long-term liabilities: Other Long-Term Liabilities (1) At September 30 2020 2019 Interest rate swap liabilities $ 1,927 $ 1,676 Operating lease liabilities 171 — Currency swap liabilities 123 193 EnergyRight® financing obligation 78 90 Paradise pipeline financing obligation — 80 Accrued long-term service agreements 56 66 Other 193 203 Total other long-term liabilities $ 2,548 $ 2,308 Note (1) Due to the implementation of the new lease accounting standard effective October 1, 2019, TVA reclassified $182 million of finance leases from Other long-term liabilities to Finance lease liabilities in the Consolidated Balance Sheet for the year ending September 30, 2019. 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, Accrued interest, and Other long-term liabilities on the Consolidated Balance Sheets. As of September 30, 2020 and 2019, the carrying amount of the interest rate swap liabilities reported in Accounts payable and accrued liabilities and Accrued interest was approximately $114 million and $88 million, respectively. See Note 15 — Risk Management Activities and Derivative Transactions — Derivatives Not Receiving Hedge Accounting Treatment — Interest Rate Derivative s for information regarding the interest rate swap liabilities. As of September 30, 2020, Interest rate swap liabilities increased $277 million as compared to September 30, 2019, primarily due to a decrease in interest rates resulting in higher 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 ® 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. As of September 30, 2020 and 2019, the carrying amount of the financing obligation reported in Accounts payable and accrued liabilities was approximately $19 million and $23 million, respectively. See Note 8 — Other Long-Term Assets for information regarding the associated loans receivable. In response to the COVID-19 pandemic, customers experiencing financial hardship can request a deferral of EnergyRight ® loan payments for a period of up to six months. This deferral option began April 20, 2020, and is available through October 31, 2020. Deferred loans will not accrue interest during the deferral months. These deferred loans have resulted in a less than $1 million impact to TVA. 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 Facility. TVA had been accounting for the contract covering this arrangement as a financing transaction due to failed sale-leaseback treatment. The contract was revised during the fourth quarter of 2020 and is no longer deemed to contain a lease component. Accordingly, amounts related to the pipeline asset and financing obligation recorded in connection with this transaction were derecognized as of September 30, 2020. The current and long-term portions of less than $1 million and $80 million, respectively, of the financing obligation are reported in Accounts payable and accrued liabilities and Other long-term liabilities, respectively, on TVA's Consolidated Balance Sheet at September 30, 2019. 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. As of September 30, 2020 and 2019, related liabilities of $15 million and $12 million, respectively, were recorded in Accounts payable and accrued liabilities.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Sep. 30, 2020
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations During the year ended September 30, 2020, TVA's total ARO liability increased $1.2 billion. To estimate its decommissioning obligation related to its nuclear generating stations, TVA uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimations and assumptions. Those assumptions include (1) estimates of the cost of decommissioning; (2) the method of decommissioning and the timing of the related cash flows; (3) the license period of the nuclear plant, considering the probability of license extensions; (4) cost escalation factors; and (5) the credit adjusted risk free rate to measure the obligation at the present value of the future estimated costs. TVA has ascribed probabilities to two different decommissioning methods related to its nuclear decommissioning obligation estimate: the DECON method and the SAFSTOR method. The DECON method requires radioactive contamination to be removed from a site and safely disposed of or decontaminated to a level that permits the site to be released for unrestricted use shortly after it ceases operation. The SAFSTOR method allows nuclear facilities to be placed and maintained in a condition that allows the facilities to be safely stored and subsequently decontaminated to levels that permit release for unrestricted use. TVA bases its nuclear decommissioning estimates on site-specific cost studies. The most recent study was approved and implemented in September 2017. An increase of $250 million was recorded to the nuclear AROs as a result of the updates. Site-specific cost studies are updated for each of TVA's nuclear units at least every five years. TVA also has decommissioning obligations related to its non-nuclear generating sites, ash impoundments, transmission substation and distribution assets, and certain general facilities. To estimate its decommissioning obligation related to these assets, TVA uses estimations and assumptions for the amounts and timing of future expenditures and makes judgments concerning whether or not such costs are considered a legal obligation. Those assumptions include (1) estimates of the costs of decommissioning, (2) the method of decommissioning and the timing of the related cash flows, (3) the expected retirement date of each asset, (4) cost escalation factors, and (5) the credit adjusted risk free rate to measure the obligation at the present value of the future estimated costs. TVA bases its decommissioning estimates for each asset on its identified preferred closure method. During 2020, the revisions in non-nuclear es timates increased $1.1 billion for the year ended September 30, 2020. 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 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, 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. In June 2020, based on recent project cost data and estimates, TVA revised its AROs for closure-by-removal of certain CCR facilities at Allen Fossil Plant, resulting in an increase to AROs of $273 million. In September 2020, TVA completed an engineering review of its cost estimates to close the ash pond complex at Gallatin Fossil Plant, resulting in an increase of $173 million due to expected cost increases for excavation, disposal, and other activities required in a closure-by-removal project. Also in September 2020, TVA completed a study of its plant decommissioning obligations and CCR post-closure care and monitoring obligations. TVA increased its plant decommissioning obligations by $19 million, primarily due to asbestos and hazardous material abatement costs. TVA increased its CCR post-closure care and monitoring AROs primarily as a result of expected cost increases to monitor groundwater and maintain CCR areas after closure as well as increases in expected acreage to maintain after closure, totaling $460 million. During 2019, the revisions in non-nuclear estimates increased $50 million for the year ended September 30, 2019. As a result of recent experience in completing settlements at certain facilities, costs for asbestos abatement activities across TVA's fossil fleet increased $114 million. TVA changed the preferred closure method for Allen West Impoundment from closure-in-place to closure-by-removal, which resulted in a cost increase of $33 million. Partially offsetting these increases was a $57 million decrease in costs for Paradise closure projects, and a $44 million decrease in costs for the Allen East Impoundment closure project. Additionally, as a result of the decision in TVA's favor by the Sixth Circuit in the lawsuit brought by TSRA and TCWN, as well as the June 2019 consent order filed in the case brought by TDEC, Gallatin discounted cash flows related to CCR closure and post-closure costs of $672 million have been recorded as Asset retirement obligations. The obligation is based upon the assumptions outlined in the consent order, including a new lined facility will be permitted and constructed on the Gallatin site and existing CCR materials in the existing wet ash disposal impoundments at Gallatin will be moved to this new facility over a 20-year period. Additionally, during the years ended September 30, 2020 and 2019, both the nuclear and non-nuclear liabilities were increased by periodic accretion, partially offset by settlement projects that were conducted during these periods. The nuclear and non-nuclear accretion amounts were deferred as regulatory assets. During 2020, 2019, and 2018, $169 million, $144 million, and $144 million, respectively, of the related regulatory assets were amortized into expense as these amounts were collected in rates. See Note 9 — Regulatory Assets and Liabilities . TVA maintains investment trusts to help fund its decommissioning obligations. See Note 16 — Fair Value Measurements — Investment Funds and Note 22 — Commitments and Contingencies — Decommissioning Costs for a discussion of the trusts' objectives and the current balances of the trusts. Asset Retirement Obligation Activity Nuclear Non-Nuclear Total Balance at September 30, 2018 $ 2,989 $ 1,790 $ 4,779 Settlements (7) (82) (89) Revisions in estimate — 50 50 Additional obligations 18 — 18 Gallatin CCR — 672 672 Accretion (recorded as regulatory asset) 136 50 186 Balance at September 30, 2019 3,136 2,480 5,616 (1) Settlements (1) (113) (114) Revisions in estimate — 1,077 1,077 Accretion (recorded as regulatory asset) 143 63 206 Balance at September 30, 2020 $ 3,278 $ 3,507 $ 6,785 (1) Note (1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Debt and Other Obligations

Debt and Other Obligations	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt and Other Obligations	Debt and Other Obligations General The TVA Act authorizes TVA to issue Bonds in an amount not to exceed $30.0 billion at any time. At September 30, 2020, TVA had only two types of Bonds outstanding: power bonds and discount notes. Power bonds have maturities between one and 50 years, and discount notes have maturities of less than one year. Power bonds and discount notes are both issued pursuant to Section 15d of the TVA Act and pursuant to the Basic Tennessee Valley Authority Power Bond Resolution adopted by the TVA Board on October 6, 1960, as amended on September 28, 1976, October 17, 1989, and March 25, 1992 (the "Basic Resolution"). Bonds are not obligations of the U.S., and the U.S. does not guarantee the payments of principal or interest on Bonds. Power bonds and discount notes rank on parity and have first priority of payment from net power proceeds, which are defined as the remainder of TVA's gross power revenues after deducting the costs of operating, maintaining, and administering its power properties and tax equivalent payments, but before deducting depreciation accruals or other charges representing the amortization of capital expenditures, plus the net proceeds from the sale or other disposition of any power facility or interest therein. TVA considers its scheduled rent payments under its leaseback transactions, as well as its scheduled payments under its lease financing arrangements involving John Sevier CCF and Southaven CCF, as costs of operating, maintaining, and administering its power properties. Costs of operating, maintaining, and administering TVA's power properties have priority over TVA's payments on the Bonds. Once net power proceeds have been applied to payments on power bonds and discount notes as well as any other Bonds that TVA may issue in the future that rank on parity with or subordinate to power bonds and discount notes, Section 2.3 of the Basic Resolution provides that the remaining net power proceeds shall be used only for (1) minimum payments into the U.S. Treasury required by the TVA Act as repayment of, and as a return on, the Power Program Appropriation Investment; (2) investment in power system assets; (3) additional reductions of TVA's capital obligations; and (4) other lawful purposes related to TVA's power business. The TVA Act and the Basic Resolution each contain two bond tests: the rate test and the bondholder protection test. Under the rate test, TVA must charge rates for power which will produce gross revenues sufficient to provide funds for, among other things, debt service on outstanding Bonds. As of September 30, 2020, TVA was in compliance with the rate test. See Note 1 — Summary of Significant Accounting Policies — General. Under the bondholder protection test, TVA must, in successive five-year periods, use an amount of net power proceeds at least equal to the sum of (1) the depreciation accruals and other charges representing the amortization of capital expenditures and (2) the net proceeds from any disposition of power facilities for either the reduction of its capital obligations (including Bonds and the Power Program Appropriation Investment) or investment in power assets. TVA met the bondholder protection test for the five-year period ended September 30, 2020, and must next meet the bondholder protection test for the five-year period ending September 30, 2025 . Secured Debt of VIEs On August 9, 2013, SCCG issued secured notes totaling $360 million that bear interest at a rate of 3.846 percent. The SCCG notes require amortizing semi-annual payments on each February 15 and August 15, and mature on August 15, 2033. Also on August 9, 2013, SCCG issued $40 million of membership interests subject to mandatory redemption. The proceeds from the secured notes issuance and the issuance of the membership interests were paid to TVA in accordance with the terms of the Southaven head lease. See Note 10 — Variable Interest Entities — Southaven VIE . TVA used the proceeds from the transaction primarily to fund the acquisition of the Southaven CCF from SSSL. On January 17, 2012, JSCCG issued secured notes totaling $900 million in aggregate principal amount that bear interest at a rate of 4.626 percent. Also on January 17, 2012, Holdco issued secured notes totaling $100 million that bear interest at a rate of 7.1 percent. The JSCCG notes and the Holdco notes require amortizing semi-annual payments on each January 15 and July 15, and mature on January 15, 2042. The Holdco notes require a $10 million balloon payment upon maturity. See Note 10 — Variable Interest Entities — John Sevier VIEs . TVA used the proceeds from the transaction to meet its requirements under the TVA Act. Secured debt of VIEs, including current maturities, outstanding at both September 30, 2020 and 2019 totaled $1.1 billion. Secured Notes On July 20, 2016, TVA acquired two entities, in a business combination, designed to administer rent payments TVA makes under certain of its lease/leaseback arrangements. On September 27, 2000, the entities issued secured notes totaling $255 million that had an interest rate of 7.299 percent and required amortizing semi-annual payments on each March 15 and September 15 with a maturity date of March 15, 2019. In 2016, TVA assumed these secured notes in the acquisition at a fair value of $78 million. The secured notes of the entities were paid in full in 2019. On September 20, 2017, TVA acquired two entities, in an asset acquisition, designed to administer rent payments TVA makes under certain of its lease/leaseback arrangements. On November 14, 2001, the entities issued secured notes totaling $272 million that had an interest rate of 5.572 percent and required amortizing semi-annual payments on each May 1 and November 1 with a maturity date of May 1, 2020. In 2017, TVA assumed these secured notes in the acquisition at a fair value of $74 million. The secured notes of the entities, including current maturities, outstanding at September 30, 2019, totaled approximately $23 million, and are included in Notes payable on TVA's Consolidated Balance Sheet. The secured notes of the entities were paid in full in 2020. Short-Term Debt The following table provides information regarding TVA's short-term borrowings: Short-term Borrowings At September 30 2020 2019 2018 Gross amount outstanding - discount notes $ 57 $ 922 $ 1,217 Weighted average interest rate - discount notes 0.06 % 2.15 % 2.05 % Put and Call Options At September 30, 2019, bond issues of $357 million held by the public were redeemable in whole or in part, at TVA's option, on call dates through 2020 and at call prices of 100 percent of the principal amount. Nine of these bond issues totaling $217 million, with maturity dates ranging from 2025 to 2043, included a "survivor's option," which allowed for right of redemption upon the death of a beneficial owner in certain specified circumstances. These bonds were classified as long-term at September 30, 2019. TVA subsequently announced in October 2019 that $217 million of callable bonds were redeemed at par on November 15, 2019. Additionally, TVA has two issues of Putable Automatic Rate Reset Securities ("PARRS") outstanding. After a fixed-rate period of five years, the coupon rate on the PARRS may automatically be reset downward under certain market conditions on an annual basis. The coupon rate reset on the PARRS is based on a calculation. For both series of PARRS, the coupon rate will reset downward on the reset date if the rate calculated is below the then-current coupon rate on the Bond. The calculation dates, potential reset dates, and terms of the calculation are different for each series. The coupon rate on the 1998 Series D PARRS may be reset on June 1 (annually) if the sum of the five-day average of the 30-Year Constant Maturity Treasury ("CMT") rate for the week ending the last Friday in April, plus 94 basis points, is below the then-current coupon rate. The coupon rate on the 1999 Series A PARRS may be reset on May 1 (annually) if the sum of the five-day average of the 30-Year CMT rate for the week ending the last Friday in March, plus 84 basis points, is below the then-current coupon rate. The coupon rates may only be reset downward, but investors may request to redeem their Bonds at par value in conjunction with a coupon rate reset for a limited period of time prior to the reset dates under certain circumstances. The coupon rate for the 1998 Series D PARRS, which mature in June 2028, has been reset eight times, from an initial rate of 6.750 percent to the current rate of 2.134 percent. In connection with these resets, $318 million of the Bonds have been redeemed; therefore, $256 million of the Bonds were outstanding at September 30, 2020. The coupon rate for the 1999 Series A PARRS, which mature in May 2029, has been reset seven times, from an initial rate of 6.50 percent to the current rate of 2.216 percent. In connection with these resets, $316 million of the Bonds have been redeemed; therefore, $208 million of the Bonds were outstanding at September 30, 2020. Due to the contingent nature of the put option on the PARRS, TVA determines whether the PARRS should be classified as long-term debt or current maturities of long-term debt by calculating the expected reset rate for the Bonds on the calculation dates, described above. If the determination date for reset is before the balance sheet date of the reporting period and the expected reset rate is less than the then-current coupon rate on the PARRS, the PARRS are included in current maturities. Otherwise, the PARRS are included in long-term debt. Debt Securities Activity The table below summarizes the long-term debt securities activity for the years ended September 30, 2020 and 2019. Debt Securities Activity For the years ended September 30 2020 2019 Issues 2020 Series A (1) $ 1,000 $ — Discount on debt issues (3) — Total $ 997 $ — Redemptions/Maturities (2) electronotes ® $ 219 $ 5 2013 Series A 1,000 2009 Series B 28 30 2018 Series A 1,000 — 1999 Series A PARRS (TVE) 23 — 1998 Series D PARRS (TVC) 17 — 1995 Series B 140 — Total redemptions/maturities of power bonds 1,427 1,035 Notes payable 23 46 Variable interest entities 39 38 Total $ 1,489 $ 1,119 Notes (1) The 2020 Series A Bonds were issued at 99.7 percent of par. (2) All redemptions were at 100 percent of par. Debt Outstanding Total debt outstanding at September 30, 2020 and 2019, consisted of the following: Short-Term Debt CUSIP or Other Identifier Maturity Call/(Put) Date 2020 2019 Short-term debt, net of discounts $ 57 $ 922 Current maturities of long-term debt of VIEs issued at par 41 39 Current maturities of notes payable — 23 Current maturities of power bonds issued at par 880591EF5 12/15/2019 3.770% — 1 880591EF5 6/15/2020 3.770% — 27 880591EF5 12/15/2020 3.770% 1 — 880591EF5 6/15/2021 3.770% 28 — 88059TEL1 11/15/2019 2.650% — 1 88059TEL1 5/15/2020 2.650% — 1 880591EV0 3/15/2020 2.250% — 1,000 880591EL2 2/15/2021 3.875% 1,500 — 880591DC3 6/7/2021 5.805% 258 (1) — Total current maturities of power bonds issued at par 1,787 1,030 Total current debt outstanding, net $ 1,885 $ 2,014 Note (1) Includes net exchange gain from currency transactions of $73 million at September 30, 2020. Long-Term Debt At September 30 CUSIP or Other Identifier Maturity Coupon Effective Call Date 2020 Par 2019 Par Stock Exchange Listings electronotes ®(2) 5/15/2020 - 2/15/2043 2.375% - 3.625% 2/15/2015 - 2/15/2018 (5) $ — $ 217 None 880591EL2 2/15/2021 3.875% — 1,500 New York 880591DC3 6/7/2021 5.805% (3) — 246 (1) New York, Luxembourg 880591EN8 8/15/2022 1.875% 1,000 1,000 New York 880591ER9 9/15/2024 2.875% 1,000 1,000 New York 880591EW8 5/15/2025 0.750% 1,000 — New York 880591CJ9 11/1/2025 6.750% 1,350 1,350 New York, Hong Kong, Luxembourg, Singapore 880591EU2 2/1/2027 2.875% 1,000 1,000 New York 880591300 (4) 6/1/2028 2.134% 256 273 New York 880591409 (4) 5/1/2029 2.216% 208 232 New York 880591DM1 5/1/2030 7.125% 1,000 1,000 New York, Luxembourg 880591DP4 6/7/2032 6.587% (3) 323 (1) 307 (1) New York, Luxembourg 880591DV1 7/15/2033 4.700% 472 472 New York, Luxembourg 880591EF5 6/15/2034 3.770% 218 246 None 880591DX7 6/15/2035 4.650% 436 436 New York 880591CK6 4/1/2036 5.980% 121 121 New York 880591CS9 4/1/2036 5.880% 1,500 1,500 New York 880591CP5 1/15/2038 6.150% 1,000 1,000 New York 880591ED0 6/15/2038 5.500% 500 500 New York 880591EH1 9/15/2039 5.250% 2,000 2,000 New York 880591EP3 12/15/2042 3.500% 1,000 1,000 New York 880591DU3 6/7/2043 4.962% (3) 194 (1) 185 (1) New York, Luxembourg 880591CF7 7/15/2045 6.235% 7/15/2020 — 140 New York 880591EB4 1/15/2048 4.875% 500 500 New York, Luxembourg 880591DZ2 4/1/2056 5.375% 1,000 1,000 New York 880591EJ7 9/15/2060 4.625% 1,000 1,000 New York 880591ES7 9/15/2065 4.250% 1,000 1,000 New York Subtotal 18,078 19,225 Unamortized discounts, premiums, issue costs, and other (122) (131) Total long-term outstanding power bonds, net 17,956 19,094 Long-term debt of VIEs, net 1,048 1,089 Total long-term debt, net $ 19,004 $ 20,183 Notes (1) Includes net exchange gain from currency transactions of $80 million and $191 million at September 30, 2020 and 2019, respectively. (2) Includes one electronotes ® issue with partial maturities of principal for each required annual payment. (3) The coupon rate represents TVA's effective interest rate. (4) TVA PARRS, CUSIP numbers 880591300 and 880591409, may be redeemed under certain conditions. See Put and Call Options above. (5) The bonds were callable on or after the dates shown. Maturities Due in the Year Ending September 30 2021 2022 2023 2024 2025 Thereafter Total Long-term power bonds, long-term debt of VIEs, and notes payable including current maturities (1) $ 1,901 $ 1,071 $ 69 $ 1,058 $ 1,059 $ 15,957 $ 21,115 Short-term debt, net of discounts 57 — — — — — 57 Note (1) Long-term power bonds does not include non-cash items of foreign currency exchange gain of $153 million, unamortized debt issue costs of $45 million, and net discount on sale of Bonds of $77 million. Long-term debt of VIE does not include non-cash item of unamortized debt issue costs of $8 million. Credit Facility Agreements TVA 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 $1.0 billion credit facility that matures on June 13, 2023, a $1.0 billion credit facility that matures on September 28, 2023, and a $500 million credit facility that matures on February 1, 2025. 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 September 30, 2020 and 2019, there were $1.5 billion and $1.3 billion, respectively, of letters of credit outstanding under these facilities, and there were no borrowings outstanding. See Note 15 — 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 September 30, 2020 Maturity Date Facility Limit Letters of Credit Outstanding Cash Borrowings Availability December 2021 $ 150 $ 38 $ — $ 112 June 2023 1,000 432 — 568 September 2023 1,000 487 — 513 February 2025 500 500 — — Total $ 2,650 $ 1,457 $ — $ 1,193 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 for 2021 with a maturity date of September 30, 2021. 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 September 30, 2020. The availability of this credit facility may be impacted by how the U.S. government addresses the possibility of approaching its debt limit. Lease/Leasebacks TVA previously entered into leasing transactions to obtain third-party financing for 24 peaking 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. On September 30, 2020 and 2019, the outstanding le aseback obligations related to the remaining CTs and QTE were $223 million and $263 million , respectively. 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. In May 2020, TVA made final rent payments under lease/leaseback transactions involving eight additional CTs, and TVA had previously acquired the equity interest related to these transactions. Rent payments under the remaining CT lease/leaseback transactions are scheduled to be made through January 2022. TVA does 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)	12 Months Ended
	Sep. 30, 2020
Equity [Abstract]
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. For the years ended September 30, 2020 and 2019, TVA reclassified $38 million of gains and $45 million of losses, respectively, related to its cash flow hedges from AOCI to Interest expense. See Note 15 — 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 9 — Regulatory Assets and Liabilities for a schedule of regulatory assets and liabilities. See Note 15 — 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 16 — Fair Value Measurements for a discussion of the recognition of certain investment fund gains and losses as regulatory assets and liabilities. See Note 21 — 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	12 Months Ended
	Sep. 30, 2020
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 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. During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts because these contracts no longer meet the criteria of net settlement. As a result, the associated $10 million net derivative liabilities have been derecognized. TVA suspended its FTP in 2014 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 is currently reevaluating 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) For the years ended September 30 Derivatives in Cash Flow Hedging Relationship Objective of Hedge Transaction Accounting for Derivative 2020 2019 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 $ (1) $ (114) 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 For the years ended September 30 Derivatives in Cash Flow Hedging Relationship 2020 2019 Currency swaps $ 38 $ (45) 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 $27 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) For the years ended September 30 Derivative Type Objective of Derivative (2) Accounting for Derivative Instrument 2020 2019 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 $ (97) $ (79) 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 (1) — Notes (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 years ended September 30, 2020 and 2019. (2) During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts. Fair Values of TVA Derivatives At September 30 2020 2019 Derivatives That Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Currency swaps £200 million Sterling $ (78) Accounts payable and accrued liabilities $(78) $ (90) Accounts payable and accrued liabilities $(6); Other long-term liabilities $(84) £250 million Sterling (63) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(58) (61) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(56) £150 million Sterling (68) Accounts payable and accrued liabilities $(3); Other long-term liabilities $(65) (57) Accounts payable and accrued liabilities $(4); Other long-term liabilities $(53) Derivatives That Do Not Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Interest rate swaps $1.0 billion notional $ (1,449) Accounts payable and accrued liabilities $(43); Accrued interest $(37); Other long-term liabilities $(1,369) $ (1,261) Accounts payable and $476 million notional (588) Accounts payable and accrued liabilities $(22); Accrued interest $(10); Other long-term liabilities $(556) (498) Accounts payable and $42 million notional (4) Accounts payable and accrued liabilities $(2); Other long-term liabilities $(2) (5) Accounts payable and Commodity contract derivatives 46 Other current assets $26; Other long-term assets $23; Accounts payable and accrued liabilities $(3) (41) Other current assets $12; Other long-term liabilities $(16); Accounts payable and accrued liabilities $(37) 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 occurred. TVA had the following currency swaps outstanding at September 30, 2020: Currency Swaps Outstanding September 30, 2020 Effective Date of Currency Swap Contract Associated TVA Bond Issues Currency Exposure Expiration Date of Swap Overall Effective 1999 £200 million 2021 5.81% 2001 £250 million 2032 6.59% 2003 £150 million 2043 4.96% 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 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, Accrued interest, and Other long-term liabilities on the Consolidated Balance Sheets, and realized gains and losses, if any, are included in TVA's Consolidated Statements of Operations. For the years ended September 30, 2020 and 2019, the changes in fair market value of the interest rate swaps resulted in the deferral of unrealized losses of $272 million and $565 million, respectively. TVA may hold short-term debt balances lower than the notional amount of the interest rate swaps from time to time due to changes in business conditions and other factors. While actual balances vary, TVA generally plans to maintain average balances of short-term debt equal to or in excess of the combined notional amount of the interest rate swaps. Commodity Derivatives . TVA enters into certain commodity contracts for coal and natural gas that require physical delivery of the contracted quantity of the commodity. During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts. TVA marks to market natural gas contracts and defers the fair market values as regulatory assets or liabilities on a gross basis. At September 30, 2020, TVA's natural gas contract derivatives had terms of up to four years. Commodity Contract Derivatives At September 30 2020 2019 Number of Contracts Notional Amount Fair Value (MtM) Number of Contracts Notional Amount Fair Value ( MtM ) Coal contract derivatives — — million tons $ — 8 9 million tons $ (4) Natural gas contract derivatives 42 302 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 September 30, 2020 and 2019, are shown in the table below. Derivative Assets and Liabilities (1) (in millions) At September 30, 2020 At September 30, 2019 Assets Commodity derivatives not subject to master netting or similar arrangement $ 49 $ 12 Liabilities Currency swaps (2) $ 209 $ 208 Interest rate swaps (2) 2,041 1,764 Total derivatives subject to master netting or similar arrangement 2,250 1,972 Commodity derivatives not subject to master netting or similar arrangement 3 53 Total liabilities $ 2,253 $ 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 September 30, 2020 or 2019. (2) Letters of credit of approximately $1.5 billion and $1.3 billion were posted as collateral at September 30, 2020 and 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 NDT, ART, SERP, and DCP. See Note 16 — 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 September 30, 2020 and 2019, the NDT held investments in forward contracts to purchase debt securities. The fair values of these derivatives were in net asset positions totaling $13 million and $22 million at September 30, 2020 and 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 September 30, 2020, the aggregate fair value of all derivative instruments with credit-risk related contingent features that were in a liability position was $2.2 billion. TVA's collateral obligations at September 30, 2020, under these arrangements, were approximately $1.5 billion, for which TVA had posted approximately $1.5 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. 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 $1.4 billion and $1.6 billion of receivables from power sales outstanding at September 30, 2020 and 2019, respectively, nearly all counterparties were rated investment grade. The obligations of customers that are not investment grade are secured by collateral. TVA 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 collectively accounted for 17 percent of total operating revenue for the years ended both September 30, 2020 and September 30, 2019. Suppliers. TVA assesses potential supplier performance risks, including procurement of fuel, parts, and services. If suppliers are unable to perform under TVA's existing contracts or if TVA is unable to obtain similar services from other vendors, TVA could experience delays, disruptions, additional costs, or other operational outcomes that may impact generation, maintenance, and capital programs. 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. Natural Gas . TVA purchases the majority of its natural gas requirements from a variety of suppliers under primarily short-term contracts. In the event of nonperformance by these suppliers, TVA believes that it can obtain replacement natural gas. Coal . To help ensure a reliable supply of coal, TVA had coal contracts with multiple suppliers at September 30, 2020. The contracted supply of coal is sourced from multiple geographic regions of the United States 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, including impacts from the COVID-19 pandemic, could result in consolidations, additional bankruptcies, restructuring, contract renegotiations, or other scenarios. Nuclear Fuel . 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 and nuclear fuel services can be obtained, although at prices that may be unfavorable when compared to the prices under the current supply agreements. Purchased Power . 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. Other Suppliers . At this time, TVA has experienced minimal impacts due to force majeure events, with the exception of a manufacturing delay for a major turbine component. A mitigation strategy was developed by TVA and the vendor to reduce projected delays and impacts to TVA's outage schedule. TVA will continue to monitor the supply base and remain in contact with suppliers to identify potential risks. Derivative Counterparties . TVA 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 September 30, 2020, 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 natural gas contracts as derivatives. See Derivatives Not Receiving Hedge Accounting Treatment

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2020
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 September 30, 2020, Investment funds were comprised 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 $2.2 billion and $866 million, respectively, at September 30, 2020. 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 to future periods. 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 limited partnerships in private equity of $218 million, private real assets of $67 million, and private credit of $33 million at September 30, 2020. The ART had unfunded commitments related to limited partnerships in private equity of $133 million, private real assets of $54 million, and private credit of $16 million at September 30, 2020. 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 NAV 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) At or for the years ended September 30 Fund Financial Statement Presentation 2020 2019 NDT Regulatory asset $ 37 $ (112) ART Regulatory asset 32 (70) SERP Other income (expense) 3 — DCP Other income (expense) 2 (2) Due to higher volatility in the financial markets associated with the COVID-19 pandemic, TVA has experienced fluctuations related to its ART and NDT investment portfolio during 2020. The losses experienced during the three months ended March 31, 2020, have been recovered. For the year ended September 30, 2020, the NDT increased in value $123 million compared to the year ended September 30, 2019. Despite this volatility, TVA's NDT funding as of September 30, 2020, continues to be fully funded per the NRC funding requirements. Currency and Interest Rate Derivatives See Note 15 — 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 See Note 15 — Risk Management Activities and Derivative Transactions — Derivatives Not Receiving Hedge Accounting Treatment. Most of these contracts are valued based on market approaches which utilize short-term and mid-term market-quoted prices from an external industry brokerage service. 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 2019) 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 assets and a $1 million decrease in the fair value of liabilities at September 30, 2020. 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 September 30, 2020 and 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 At September 30, 2020 Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 500 $ — $ — $ 500 Government debt securities (1) 485 40 — 525 Corporate debt securities (2) — 356 — 356 Mortgage and asset-backed securities — 27 — 27 Institutional mutual funds 188 — — 188 Forward debt securities contracts — 13 — 13 Private equity funds measured at net asset value (3) — — — 194 Private real asset funds measured at net asset value (3) — — — 168 Private credit measured at net asset value (3) — — — 53 Commingled funds measured at net asset value (3) — — — 1,174 Total investments 1,173 436 — 3,198 Commodity contract derivatives — 49 — 49 Total $ 1,173 $ 485 $ — $ 3,247 Quoted Prices in Active Markets for Identical Liabilities Significant Other Significant Total Liabilities Currency swaps (4) $ — $ 209 $ — $ 209 Interest rate swaps — 2,041 — 2,041 Commodity contract derivatives — 3 — 3 Total $ — $ 2,253 $ — $ 2,253 Notes (1) Includes government-sponsored entities. (2) Includes both U.S. and foreign debt. (3) 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. (4) 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 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . Fair Value Measurements At September 30, 2019 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 asset 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 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 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts. TVA previously used internal valuation specialists for the calculation of its commodity contract derivatives fair value measurements classified as Level 3. Analytical testing was 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 Balance at October 1, 2018 $ 58 Change in net unrealized gains (losses) deferred as regulatory assets and liabilities (62) Balance at September 30, 2019 (4) Settlements (1) Change in net unrealized gains (losses) deferred as regulatory assets and liabilities 5 Balance at September 30, 2020 $ — 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 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 instruments. The fair value of the financial instruments held at September 30, 2020 and 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 September 30, 2020 and 2019, were as follows: Estimated Values of Financial Instruments Not Recorded at Fair Value At September 30, 2020 At September 30, 2019 Valuation Classification Carrying Fair Carrying Fair EnergyRight ® receivables (including current portion) Level 2 $ 87 $ 86 $ 101 $ 100 Loans and other long-term receivables, net (including current portion) Level 2 $ 105 $ 93 $ 131 $ 120 EnergyRight ® financing obligations (including current portion) Level 2 $ 97 $ 108 $ 113 $ 126 Unfunded loan commitments Level 2 $ — $ 2 $ — $ 10 Membership interests of VIEs subject to mandatory redemption (including current portion) Level 2 $ 26 $ 35 $ 28 $ 37 Long-term outstanding power bonds (including current maturities), net Level 2 $ 19,743 $ 26,630 $ 20,124 $ 26,059 Long-term debt of VIEs (including current maturities), net Level 2 $ 1,089 $ 1,419 $ 1,128 $ 1,371 Long-term notes payable (including current maturities) Level 2 $ — $ — $ 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.

Proprietary Capital (Text Block

Proprietary Capital (Text Block)	12 Months Ended
	Sep. 30, 2020
Stockholders' Equity Note [Abstract]
Proprietary Capital	Proprietary Capital Appropriation Investment TVA's power program and stewardship (nonpower) programs were originally funded primarily by appropriations from Congress. In 1959, Congress passed an amendment to the TVA Act that required TVA's power program to be self-financing from power revenues and proceeds from power program financings. While TVA's power program did not directly receive appropriated funds after it became self-financing, TVA continued to receive appropriations for certain multipurpose and other nonpower mission-related activities as well as for its stewardship activities. TVA has not received any appropriations from Congress for any activities since 1999, and since that time, TVA has funded stewardship program activities primarily with power revenues. The 1959 amendment to the TVA Act also required TVA, beginning in 1961, to make annual payments to the U.S. Treasury from net power proceeds as a repayment of and as a return on the Power Program Appropriation Investment until a total of $1.0 billion of the Power Program Appropriation Investment has been repaid in accordance with the 1959 amendment. TVA fulfilled its requirement to repay $1.0 billion of the Power Program Appropriation Investment in 2014. The TVA Act requires TVA to continue making payments to the U.S. Treasury as a return on the remaining $258 million of the Power Program Appropriation Investment. The table below summarizes TVA's activities related to appropriated funds and retained earnings. Summary of Proprietary Capital Activity At or for the years ended September 30 2020 2019 Power Program Nonpower Power Program Nonpower Appropriation Investment $ 258 $ 4,351 $ 258 $ 4,351 Proprietary Capital Balance at beginning of year 10,823 (3,795) 9,404 (3,787) Net income (loss) for year 1,360 (8) 1,425 (8) Return on power program appropriation investment (6) — (6) — Balance at end of year 12,177 (3,803) 10,823 (3,795) Net proprietary capital at September 30 $ 12,435 $ 548 $ 11,081 $ 556 Payments to the U.S. Treasury TVA paid the U.S. Treasury $6 million, $6 million, and $5 million in 2020, 2019, and 2018, respectively, as a return on the Power Program Appropriation Investment. The amount of the return on the Power Program Appropriation Investment is based on the Power Program Appropriation Investment balance at the beginning of that year and the computed average interest rate payable by the U.S. Treasury on its total marketable public obligations at the same date. The interest rates payable by TVA on the Power Program Appropriation Investment were 2.44 percent, 2.37 percent, and 2.09 percent for 2020, 2019, and 2018, respectively. Accumulated Other Comprehensive Income (Loss) The items included in AOCI consist of market valuation adjustments for certain derivative instruments. See Note 15 — Risk Management Activities and Derivative Transactions .

Other Income (Expense), Net

Other Income (Expense), Net	12 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Other Income (Expense), Net	Other Income (Expense), Net Income and expenses not related to TVA's operating activities are summarized in the following table: Other Income (Expense), Net For the years ended September 30 2020 2019 2018 Bellefonte deposit $ — $ 21 $ — Interest income 18 25 23 External services 12 13 14 Gains (losses) on investments 9 3 6 Miscellaneous (3) — 7 Total other income (expense), net $ 36 $ 62 $ 50 During 2020, Other income (expense), net decreased $26 million, primarily driven by $21 million of other income in 2019 related to a deposit liability received by TVA as a down payment on the sale of Bellefonte. The purchaser, Nuclear Development, LLC, failed to fulfill the requirements of the sales contract with respect to obtaining 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. Additionally, Interest income decreased $7 million primarily as a result of lower interest rates. See Note 22 — Commitments and Contingencies — Legal Proceedings for a discussion of the lawsuit filed by Nuclear Development, LLC.

Related Parties

Related Parties	12 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Parties	Related Parties TVA is a wholly-owned corporate agency of the federal government, and because of this relationship, TVA's revenues and expenses are included as part of the federal budget as a revolving fund. TVA's purpose and responsibilities as an agency are described under the "Other Agencies" section of the federal budget. TVA currently receives no appropriations from Congress and funds its business using power system revenues, power financings, and other revenues. TVA is a source of cash to the federal government. TVA will indefinitely continue to pay the U.S. Treasury a return on the outstanding $258 million of the government's appropriation investment in TVA's power facilities (the "Power Program Appropriation Investment"). See Note 18 — Proprietary Capital — Appropriation Investment. TVA also has access to a financing arrangement with the U.S. Treasury pursuant to the TVA Act. TVA and the U.S. Treasury entered into a memorandum of understanding under which the U.S. Treasury provides TVA with a $150 million credit facility. This credit facility has a maturity date of September 30, 2021, and is typically renewed annually. Access to this credit facility or other similar financing arrangements has been available to TVA since the 1960s. See Note 13 — Debt and Other Obligations — Credit Facility Agreements. In the normal course of business, TVA contracts with other federal agencies for sales of electricity and other services. Transactions with agencies of the federal government were as follows: Related Party Transactions For the years ended, or at, September 30 2020 2019 2018 Revenue from sales of electricity $ 105 $ 118 $ 122 Other income 260 258 240 Expenditures Operating expenses 224 222 220 Additions to property, plant, and equipment 9 10 8 Cash and cash equivalents 31 45 46 Accounts receivable, net 94 76 60 Investment funds 485 279 199 Long-term accounts receivable 27 53 46 Accounts payable and accrued liabilities 39 69 69 Long-term power bonds, net 1 — — Return on power program appropriation investment 6 6 5

Unaudited Quarterly Financial I

Unaudited Quarterly Financial Information	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Financial Information	24. Unaudited Quarterly Financial Information A summary of the unaudited quarterly results of operations for the years 2020 and 2019 follows. This summary should be read in conjunction with the audited consolidated financial statements appearing herein. Results for interim periods may fluctuate as a result of seasonal weather conditions, changes in rates, and other factors. Unaudited Quarterly Financial Information 2020 First Second Third Fourth Total Operating revenues $ 2,578 $ 2,521 $ 2,251 $ 2,899 $ 10,249 Operating expenses 2,046 1,914 1,716 1,862 7,538 Operating income 532 607 535 1,037 2,711 Net income (loss) 192 255 205 700 1,352 Unaudited Quarterly Financial Information 2019 First Second Third Fourth Total Operating revenues $ 2,725 $ 2,750 $ 2,604 $ 3,239 $ 11,318 Operating expenses 1,960 2,158 2,088 2,301 8,507 Operating income 765 592 516 938 2,811 Net income (loss) 423 241 165 588 1,417

Revenue

Revenue	12 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	Revenue TVA adopted Revenue from Contracts with Customers effective October 1, 2018, using the modified retrospective method of adoption, which does not require restatement of prior year reported results. As a result of the adoption of this standard, no cumulative effect adjustment was recorded. Additionally, comparative disclosures for 2018 operating results with the previous revenue recognition rules are not applicable as TVA's revenue recognition has not materially changed as a result of the new standard. 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. 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 In 2020, the revenues generated from TVA's electricity sales were $10.1 billion and accounted for virtually all of TVA's revenues. TVA's revenues by state for each of the last three years are detailed in the table below: Operating Revenues By State For the years ended September 30 (in millions) 2020 2019 2018 Alabama $ 1,439 $ 1,593 $ 1,600 Georgia 249 270 267 Kentucky 624 691 696 Mississippi 941 1,063 1,052 North Carolina 65 74 66 Tennessee 6,740 7,419 7,350 Virginia 42 45 48 Subtotal 10,100 11,155 11,079 Off-system sales 4 4 7 Revenue capitalized during pre-commercial plant operations (1) — — (11) Revenue from sales of electricity 10,104 11,159 11,075 Other revenue 145 159 158 Total operating revenues $ 10,249 $ 11,318 $ 11,233 Note (1) Represents revenue capitalized during pre-commercial operations of $11 million at Allen CC in 2018. See Note 1 — Summary of Significant Accounting Policies — Pre-Commercial Plant Operations . TVA's operating revenues by customer type for each of the last three years are detailed in the table below: Operating Revenues by Customer Type For the years ended September 30 (in millions) 2020 2019 2018 Revenue from sales of electricity Local power companies (1) $ 9,406 $ 10,351 $ 10,262 Industries directly served 588 686 695 Federal agencies and other 110 122 129 Revenue capitalized during pre-commercial plant operations (2) — — (11) Revenue from sales of electricity 10,104 11,159 11,075 Other revenue 145 159 158 Total operating revenues $ 10,249 $ 11,318 $ 11,233 Notes (1) The amount for the years ended September 30, 2020 and 2019, is net of $163 million and $14 million, respectively, of wholesale bill credits to LPCs participating in the long-term Partnership Agreement. There were no such credits in 2018. (2) Represents revenue capitalized during pre-commercial operations of $11 million at Allen CC in 2018. See Note 1 — Summary of Significant Accounting Policies — Pre-Commercial Plant Operations . TVA and LPCs continue to work together to meet the changing needs of consumers around the Tennessee Valley. In 2019, 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 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 June 2020, TVA provided participating LPCs a flexibility option that allows them to locally generate up to approximately five percent of average total hourly energy sales over the prior five years in order to meet their individual customers' needs. As of November 16, 2020, 142 LPCs had signed the 20-year Partnership Agreement with TVA, and 64 LPCs had signed a Flexibility Agreement. In August 2020, the TVA Board approved a $200 million Pandemic Relief Credit. The 2.5 percent base rate credit will be applied beginning in October 2020 and will remain in effect through the end of 2021. The credit will apply to service provided to TVA's local power company customers, their large commercial and industrial customers, and TVA directly served customers. The number of LPCs with the contract arrangements described below, the revenues derived from such arrangements during 2020, and the percentage of TVA's total operating revenues during 2020 represented by these revenues are summarized in the tables below: TVA Local Power Company Contracts At or for the year ended September 30, 2020 Contract Arrangements (1) Number of LPCs Revenue from Sales of Electricity to LPCs Percentage of Total Operating Revenues 20-year termination notice 142 $ 7,666 74.8 % 5-year termination notice 11 1,740 17.0 % Total (2) 153 $ 9,406 91.8 % Notes (1) Ordinarily, the LPCs and TVA have the same termination notice period; however, in contracts with two 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. (2) TVA wholesale power contracts decreased to 153 in 2020 due to a merger between two LPCs in July 2020. TVA's two largest LPCs — MLGW and NES — have contracts with a five-year and a 20-year termination notice period, respectively. Sales to MLGW and NES accounted for nine percent and eight percent, respectively, of TVA's total operating revenues in 2020. In May 2020, MLGW published a draft IRP to guide energy choices in the future, and in July 2020, TVA made a proposal to MLGW that highlights the benefits of remaining a TVA customer. In August 2020, MLGW published a final IRP and announced its plan to issue requests for proposal to validate the cost estimates included in the IRP. In addition, certain other LPCs are evaluating options for future energy choices. 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 as of September 30, 2020. 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. Energy Prepayment Obligations. In 2004, TVA and its largest customer, MLGW, entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 15 years. TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations. The arrangement ceased in 2019. TVA recognized approximately $100 million of noncash revenue in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as noncash revenue on a cumulative basis during the life of the agreement, $100 million of which was recognized as noncash revenue and a corresponding reduction in the balance of Energy prepayment obligations during 2018. During 2019, $10 million was recognized as noncash revenue and a corresponding reduction in the balance of Energy prepayment obligations. Discounts to account for the time value of money, which were recorded as a reduction to electricity sales, amounted to $4 million and $46 million during 2019 and 2018, respectively. Economic Development Incentives. Under certain economic development programs TVA offers incentives to existing and potential power customers in targeted business sectors that make multi-year commitments to invest in the Tennessee Valley. TVA records those incentives as reductions of revenue. In 2020 and 2019, TVA recorded a total of $318 million and $310 million, respectively, in incentives as a reduction of revenue. 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 September 30, 2020 and 2019, the outstanding unpaid incentives were $172 million and $157 million, respectively. Incentives that have been paid out may be subject to claw back if the customer fails to meet certain program requirements. Additionally, in May 2020, TVA established flexibility provisions to support the continued operations and recovery of participating customers experiencing financial and operational hardships as a result of the COVID-19 pandemic and corresponding economic downturn. These provisions have not had a material impact to TVA.

Plant Closures _Text Block_

Plant Closures [Text Block]	12 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Plant Closures	6. Plant Closures Background TVA must continuously evaluate all generating assets to ensure an optimal energy portfolio that provides safe, clean, and reliable power while maintaining flexibility and fiscal responsibility to the people of the Tennessee Valley. Based on results of assessments presented to the TVA Board in 2019, the retirement of Paradise Fossil Plant ("Paradise") Unit 3 by December 2020 and Bull Run Fossil Plant ("Bull Run") by December 2023 was approved. Subsequent to the TVA Board approval, TVA determined that Paradise would not be restarted after January 2020 due to the plant's material condition. Paradise Unit 3 was taken offline on February 1, 2020, effectively retiring the plant. Financial Impact As a result of TVA's decision to accelerate the retirements of Paradise and Bull Run, certain construction projects at these locations were identified as probable of abandonment or were no longer expected to be in service for greater than one year prior to the plants' retirement dates. The write-off of these projects resulted in $11 million and $151 million of Operating and maintenance expense during the years ended September 30, 2020 and 2019, respectively. TVA also recognized losses of $2 million and $19 million in Operating and maintenance expense related to additional materials and supplies inventory reserves and write-offs identified at Paradise during the years ended September 30, 2020 and 2019, respectively. TVA's policy is to adjust depreciation rates to reflect the most current assumptions, ensuring units will be fully depreciated by the applicable retirement dates. As a result of TVA's decision to accelerate the retirement of Paradise and Bull Run, TVA recognized an additional $387 million and $566 million of accelerated depreciation for the years ended September 30, 2020 and 2019, respectively.

Leases (Text Block)

Leases (Text Block)	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases of Lessee Disclosure	7 . Leases As described in Note 2 — Impact of New Accounting Standards and Interpretations , TVA elected the modified retrospective method of adoption for the new lease accounting standard 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. The following table provides additional information regarding the presentation of leases on the Consolidated Balance Sheets at September 30, 2020 : Amounts Recognized on TVA's Consolidated Balance Sheets At September 30, 2020 Assets Operating Operating lease assets, net of amortization $ 232 Finance Finance leases 516 Total lease assets $ 748 Liabilities Current Operating Accounts payable and accrued liabilities $ 63 Finance Accounts payable and accrued liabilities 41 Non-current Operating Other long-term liabilities 171 Finance Finance lease liabilities 525 Total lease liabilities $ 800 TVA's leases consist primarily of railcars, equipment, real estate/land, power generating facilities, and gas pipelines. TVA's leases have various terms and expiration dates remaining from less than one year to 26 years. The components of lease costs for the year September 30, 2020, were as follows: Lease Costs For the year ended September 30, 2020 Operating lease costs (1) $ 84 Variable lease costs (1) 75 Short-term lease costs (1) 7 Finance lease costs Amortization of lease assets (2) 15 Interest on lease liabilities (3)(4) 33 Total finance lease costs 48 Total lease costs $ 214 Notes (1) Costs are included in Operating and maintenance expense, Fuel expense, Purchased power expense, and Tax equivalents expense on the Consolidated Statements of Operations. TVA's rental expense for operating leases was approximately $97 million and $92 million for the years ended September 30, 2019 and 2018, respectively. (2) Expense is included in Depreciation and amortization expense on the Consolidated Statements of Operations. (3) Expense is included in Interest expense on the Consolidated Statements of Operations. (4) Certain finance leases receive regulatory accounting treatment and are reclassified to Fuel expense and Purchased power expense. TVA's variable lease costs are primarily related to renewable energy purchase agreements that require TVA to purchase all output from the underlying facility. Payments under those agreements are solely based on the actual output over the lease term. Certain TVA lease agreements contain renewal options. Those renewal options that are reasonably certain to be exercised are included in the lease measurements. The following table contains additional information with respect to cash and non-cash activities related to leases: Amounts Recognized on TVA's Consolidated Statements of Cash Flows For the Year Ended September 30, 2020 Operating cash flows for operating leases $ 85 Operating cash flows for finance leases 33 Financing cash flows for finance leases 15 Lease assets obtained in exchange for lease obligations (non-cash) Operating leases (1) $ 110 Finance leases 394 Note (1) Amount excludes operating lease assets recorded as a result of the adoption of the new lease standard. TVA has certain finance leases under PPAs under which the present value of the minimum lease payments exceeds the fair value of the related lease asset at the date of measurement. This resulted in an interest rate that was higher than TVA's incremental borrowing rate. At September 30, 2020 , the weighted average remaining lease term in years and the weighted average discount rate for TVA's operating and financing leases were as follows: Weighted Averages At September 30, 2020 Weighted average remaining lease terms Operating leases 5 years Finance leases 12 years Weighted average discount rate (1) Operating leases 1.6% Finance leases 21.8% Note (1) The discount rate is calculated using the rate implicit in a lease if it is readily determinable. If the rate used by the lessor is not readily determinable, TVA uses its incremental borrowing rate as permitted by accounting guidance. The incremental borrowing rate is influenced by TVA's credit rating and lease term and as such may differ for individual leases, embedded leases, or portfolios of leased assets. The following table presents maturities of lease liabilities and a reconciliation of the undiscounted cash flows to lease liabilities at September 30, 2020 : Future Minimum Lease Payments Minimum Payments Due at September 30, 2020 Operating leases 2021 $ 66 2022 51 2023 39 2024 37 2025 34 Thereafter 16 Minimum annual payments 243 Less: present value discount (9) Operating present value of net minimum lease payments $ 234 Finance leases 2021 $ 92 2022 93 2023 92 2024 87 2025 86 Thereafter 592 Minimum annual payments 1,042 Less: amount representing interest (476) Finance present value of net minimum lease payments $ 566 The following table presents the future minimum lease payments under operating leases and the finance lease maturities as reported under the previous lease standard at September 30, 2019: Future Minimum Lease Payments Minimum Payments Due at September 30, 2019 Operating leases 2020 $ 76 2021 75 2022 60 2023 12 2024 3 Thereafter 2 Minimum annual payments 228 Less: present value discount — Operating present value of net minimum lease payments $ 228 Finance leases 2020 $ 53 2021 53 2022 53 2023 55 2024 51 Thereafter 418 Minimum annual payments 683 Less: amount representing interest (495) Finance present value of net minimum lease payments $ 188 TVA entered into a PPA with a renewable resource provider for solar generation and rights to charge and discharge a battery energy storage system. The system is considered a lease component in this agreement. This lease has a term of 20 years, and is expected to commence on October 1, 2022. Payments made over the term of this lease are expected to total approximately $89 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies [Policy Text Block]	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
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 approximately 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 United States 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 power 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 power 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 other 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 The accompanying consolidated 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 10 — Variable Interest Entities
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, including impacts from the COVID-19 pandemic, 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.
Reclassification, Comparability Adjustment	Reclassifications Certain historical amounts have been reclassified in the accompanying consolidated financial statements to the current presentation.
Cash and Cash Equivalents and Restricted Cash and Investments	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 22 — Commitments and Contingencies — Legal Proceedings — Environmental Agreements . The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported in the Consolidated Balance Sheets and Consolidated Statements of Cash Flows: Cash, Cash Equivalents, and Restricted Cash 2020 2019 Cash and cash equivalents $ 500 $ 299 Restricted cash and cash equivalents, included in Other long-term assets 21 23 Total Cash, cash equivalents, and restricted cash $ 521 $ 322
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. TVA continues to monitor the impact of the COVID-19 pandemic on accounts and loans receivable balances to evaluate the allowance for uncollectible accounts. The allowance for uncollectible accounts was less than $1 million at both September 30, 2020 and 2019, for accounts receivable. Additionally, loans receivable of $105 million and $131 million at September 30, 2020 and 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 September 30, 2020 and 2019, respectively.
Revenues	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. Energy Prepayment Obligations In 2004, TVA and its largest customer, Memphis Light, Gas and Water Division ("MLGW"), entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 180 months. TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations. The arrangement ceased in 2019. Revenue was recognized in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as non-cash revenue on a cumulative basis during the life of the agreement, $10 million and $100 million of which was recognized as non-cash revenue during 2019 and 2018, respectively. Discounts to account for the time value of money, which are recorded as a reduction to electricity sales, amounted to $4 million and $46 million for the years ended September 30, 2019 and 2018, respectively.
Pre-Commercial Plant Operations	Pre-Commercial Plant Operations As part of the process of completing the construction of a generating unit, the electricity produced is used to serve the
Inventories	Inventories Certain Fuel, Materials, and Supplies . Materials and supplies inventories are valued using an average unit cost method. A new average cost is computed after each inventory purchase transaction, and inventory issuances are priced at the latest moving weighted average unit cost. Coal, fuel oil, and natural gas inventories are valued using an average cost method. A new weighted average cost is computed monthly, and monthly issues are priced accordingly. Renewable Energy Credits. TVA accounts for Renewable Energy Certificates ("RECs") using the specific identification cost method. RECs that are acquired through power purchases are recorded as inventory and charged to purchased power expense when the RECs are subsequently used or sold. TVA assigns a value to the RECs at the inception of the power purchase arrangement using a relative fair value approach. RECs created through TVA-owned asset generation are recorded at zero cost. Emission Allowances . TVA has emission allowances for sulfur dioxide ("SO 2 ") and nitrogen oxide ("NO x ") which are accounted for as inventory. The cost of specific allowances used each month is charged to operating expense based on tons of SO 2 and NO x emitted during the respective compliance periods. Allowances granted to TVA by the Environmental Protection Agency ("EPA") are recorded at zero cost. Allowance for Inventory Obsolescence . TVA reviews materials and supplies inventories by category and usage on a periodic basis. Each category is assigned a probability of becoming obsolete based on the type of material and historical usage data. In 2018, TVA started moving from a site-specific inventory management policy to a fleet-wide strategy for each generation type. Based on the estimated value of the inventory, TVA adjusts its allowance for inventory obsolescence.
Property, Plant, and Equipment, and Depreciation	Property, Plant, and Equipment, and Depreciation Property, Plant, and Equipment. Additions to plant are recorded at cost, which includes direct and indirect costs. The cost of current repairs and minor replacements is charged to operating expense. Nuclear fuel, which is included in Property, plant, and equipment, is valued using the average cost method for raw materials and the specific identification method for nuclear fuel in a reactor. Amortization of nuclear fuel in a reactor is calculated on a units-of-production basis and is included in fuel expense. When property, plant, and equipment is retired, accumulated depreciation is charged for the original cost of the assets. Gains or losses are only recognized upon the sale of land or an entire operating unit. 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 will be updated approximately every five years. Depreciation expense for the years ended September 30, 2020, 2019, and 2018 was $1.6 billion, $1.8 billion, and $1.3 billion, respectively. Depreciation expense expressed as a percentage of the average annual depreciable completed plant was 2.74 percent for 2020, 3.09 percent for 2019, and 2.45 percent for 2018. Average depreciation rates by asset class are as follows: Property, Plant, and Equipment Depreciation Rates At September 30 2020 2019 2018 Asset Class Nuclear 2.38 2.38 2.64 Coal-fired (1) 3.62 4.96 2.32 Hydroelectric 1.60 1.61 1.57 Gas and oil-fired 3.04 3.00 2.93 Transmission 1.34 1.34 1.32 Other 7.26 7.16 5.90 Note (1) The rates include the acceleration of depreciation related to retiring certain coal-fired units. Coal-Fired . As a result of TVA's decision to idle or retire certain units since the previous depreciation study, TVA recognized $387 million, $566 million, and $48 million in accelerated depreciation expense related to the units during the years ended September 30, 2020, 2019, and 2018, respectively. Accelerated depreciation is based on the remaining useful life of the asset at the time the decision is made to idle or retire a unit. Reacquired Rights . Property, plant, and equipment includes intangible reacquired rights, net of amortization, of $192 million and $200 million as of September 30, 2020 and 2019, respectively, related to the purchase of residual interests from lease/leaseback agreements of certain combustion turbine units ("CTs"). Reacquired rights are amortized over the estimated useful life of the underlying CTs. Amortization expense was $8 million for all years 2020, 2019, and 2018. Software Costs. TVA capitalizes certain costs incurred in connection with developing or obtaining internal-use software. Capitalized software costs are included in Property, plant, and equipment on the Consolidated Balance Sheets and are generally amortized over seven years. At September 30, 2020 and 2019, unamortized computer software costs totaled $54 million and $63 million, respectively. Amortization expense related to capitalized computer software costs was $42 million, $38 million, and $32 million for 2020, 2019, and 2018, respectively. Software costs that do not meet capitalization criteria are expensed as incurred. Impairment of Assets. TVA evaluates long-lived assets for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. For long-lived assets, TVA bases its evaluation on impairment indicators such as the nature of the assets, the future economic benefit of the assets, any historical or future profitability measurements, regulatory approval and ability to set rates at levels that allow for recoverability of the assets, and other external market conditions or factors that may be present. If such impairment indicators are present or other factors exist that indicate that the carrying amount of an asset may not be recoverable, TVA determines whether an impairment has occurred based on an estimate of undiscounted cash flows attributable to the asset as compared with the carrying value of the asset. If an impairment has occurred, the amount of the impairment recognized is measured as the excess of the asset's carrying value over its fair value. Additionally, TVA regularly evaluates construction projects. If the project is canceled or deemed to have no future economic benefit, the project is written off as an asset impairment or, upon TVA Board approval, reclassified as a regulatory asset. See Note 6 — Plant Closures
Lessee, Leases	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 ("PPAs") 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 power purchase agreements, the terms of which vary. The total lease obligation included in Accounts payable and accrued liabilities and lease liabilities related to these agreements were $500 million and $174 million for finance and operating leases, respectively, at September 30, 2020. 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 September 30, 2020. 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.
Decommissioning Costs	Decommissioning Costs TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets. These obligations relate to fossil fuel-fired generating plants, nuclear generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. These other property-related assets include, but are not limited to, easements and coal rights. Activities involved with retiring these assets could include decontamination and demolition of structures, removal and disposal of wastes, and site restoration. Revisions to the estimates of asset retirement obligations ("AROs") are made whenever factors indicate that the timing or amounts of estimated cash flows have changed materially. Any accretion or depreciation expense related to these liabilities and assets is charged to a regulatory asset. See Note 9 — Regulatory Assets and Liabilities — Nuclear Decommissioning Costs and Non-Nuclear Decommissioning Costs and Note 12 — Asset Retirement Obligations.
Down-blend Offering for Tritium	Down-blend Offering for Tritium TVA, the Department of Energy ("DOE"), and certain nuclear fuel contractors have entered into agreements, referred to as the Down-blend Offering for Tritium, that provide for the production, processing, and storage of low-enriched uranium that is to be made using surplus DOE highly enriched uranium and other uranium. Low-enriched uranium can be fabricated into fuel for use in a nuclear power plant. Production of the low-enriched uranium began in 2019 and is contracted to continue through October 2027. Beginning October 2027, contract activity will consist of storage and flag management. Flag management ensures that the uranium is of U.S. origin, free from foreign obligations, and unencumbered by policy restrictions, so that it can be used in connection with the production of tritium. Under the terms of the interagency agreement between the DOE and TVA, the DOE will reimburse TVA for a portion of the costs of converting the highly enriched uranium to low-enriched uranium. Since 2019, TVA has received $89 million in reimbursements from the DOE. At September 30, 2020, TVA recorded $6 million in Accounts receivable, net related to this agreement.
Investment Funds	Investment Funds Investment funds consist primarily of trust funds designated to fund decommissioning requirements (see Note 22 — Commitments and Contingencies — Decommissioning Costs ), the Supplemental Executive Retirement Plan ("SERP") (see Note 21 — Benefit Plans — Overview of Plans and Benefits — Supplemental Executive Retirement Plan ), and the Deferred Compensation Plan ("DCP"). The Nuclear Decommissioning Trust ("NDT") holds funds primarily for the ultimate decommissioning of TVA's nuclear power plants. The Asset Retirement Trust ("ART") holds funds primarily for the costs related to the future closure and retirement of TVA's other long-lived assets. 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 funds are all classified as trading.
Insurance	Insurance Although TVA uses private companies to administer its healthcare plans for eligible active and retired employees not covered by Medicare, TVA does not purchase health insurance. Third-party actuarial specialists assist TVA in determining certain liabilities for self-insured claims. TVA recovers the costs of claims through power rates and through adjustments to the participants' contributions to their benefit plans. These liabilities are included in Other liabilities on the Consolidated Balance Sheets. TVA sponsors an Owner Controlled Insurance Program which provides workers' compensation and liability insurance for a select group of contractors performing maintenance, modifications, outage, and new construction activities at TVA facilities. The Federal Employees' Compensation Act ("FECA") governs liability to employees for service-connected injuries. TVA purchases excess workers' compensation insurance above a self-insured retention. In addition to excess workers' compensation insurance, TVA purchases the following types of insurance: • Nuclear liability insurance; nuclear property, decommissioning, and decontamination insurance; and nuclear accidental outage insurance. See Note 22 — Commitments and Contingencies — Nuclear Insurance . • Excess liability insurance for aviation, auto, marine, and general liability exposures. • Property insurance for certain conventional (non-nuclear) assets.
Research and Development Costs	Research and Development Costs Research and development costs are expensed when incurred. TVA's research programs include those related to power delivery technologies, emerging technologies (clean energy, renewables, distributed resources, and energy efficiency), technologies related to generation (fossil fuel, nuclear, and hydroelectric), and environmental technologies.
Tax Equivalents	Tax Equivalents TVA is not subject to federal income taxation. In addition, neither TVA nor its property, franchises, or income is subject to taxation by states or their subdivisions. The TVA Act requires TVA to make payments to states and counties in which TVA conducts its power operations and in which TVA has acquired power properties previously subject to state and local taxation. The total amount of these payments is five percent of gross revenues from sales of power during the preceding year, excluding sales or deliveries to other federal agencies and off-system sales with other utilities, with a provision for minimum payments under certain circumstances. TVA calculates tax equivalent expense by subtracting the prior year fuel cost-related tax equivalent regulatory asset or liability from the payments made to the states and counties during the current year and adding back the current year fuel cost-related tax equivalent regulatory asset or liability. Fuel cost-related tax equivalent expense is recognized in the same accounting period in which the fuel cost-related revenue is recognized.
Maintenance Costs	Maintenance CostsTVA records maintenance costs and repairs related to its property, plant, and equipment in the Consolidated Statements of Operations as they are incurred except for the recording of certain regulatory assets for retirement and removal costs.

Variable Interest Entities (Pol

Variable Interest Entities (Policies)	12 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [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 as of September 30, 2020 and 2019, as reflected on the Consolidated Balance Sheets, are as follows: Summary of Impact of VIEs on Consolidated Balance Sheets At September 30 2020 2019 Current liabilities Accrued interest $ 10 $ 11 Accounts payable and accrued liabilities 3 3 Current maturities of long-term debt of variable interest entities 41 39 Total current liabilities 54 53 Other liabilities Other long-term liabilities 23 25 Long-term debt, net Long-term debt of variable interest entities, net 1,048 1,089 Total liabilities $ 1,125 $ 1,167
Consolidation, 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.

Asset Retirement Obligations As

Asset Retirement Obligations Asset Retirement Obligations (Policies)	12 Months Ended
	Sep. 30, 2020
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations, Policy	Decommissioning Costs TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets. These obligations relate to fossil fuel-fired generating plants, nuclear generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. These other property-related assets include, but are not limited to, easements and coal rights. Activities involved with retiring these assets could include decontamination and demolition of structures, removal and disposal of wastes, and site restoration. Revisions to the estimates of asset retirement obligations ("AROs") are made whenever factors indicate that the timing or amounts of estimated cash flows have changed materially. Any accretion or depreciation expense related to these liabilities and assets is charged to a regulatory asset. See Note 9 — Regulatory Assets and Liabilities — Nuclear Decommissioning Costs and Non-Nuclear Decommissioning Costs and Note 12 — Asset Retirement Obligations.

Proprietary Capital Payments to

Proprietary Capital Payments to the U.S. Treasury (Policies)	12 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Payments to U S Treasury	Payments to the U.S. Treasury TVA paid the U.S. Treasury $6 million, $6 million, and $5 million in 2020, 2019, and 2018, respectively, as a return on the Power Program Appropriation Investment. The amount of the return on the Power Program Appropriation Investment is based on the Power Program Appropriation Investment balance at the beginning of that year and the computed average interest rate payable by the U.S. Treasury on its total marketable public obligations at the same date. The interest rates payable by TVA on the Power Program Appropriation Investment were 2.44 percent, 2.37 percent, and 2.09 percent for 2020, 2019, and 2018, respectively.

Benefit Plans Benefit Plans (Po

Benefit Plans Benefit Plans (Policies)	12 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Benefit Plans	Accounting Mechanisms Regulatory Accounting. TVA has classified all amounts related to unrecognized prior service costs/(credits), net actuarial gains or losses, and the funded status as regulatory assets or liabilities as such amounts are probable of collection in future rates. Additionally, TVA recognizes pension costs as regulatory assets or regulatory liabilities to the extent that the amount calculated under U.S. GAAP as pension expense differs from the amount TVA contributes to the pension plan as pension plan contributions. As a result of recent plan design changes, future contributions are expected to exceed the expense calculated under U.S. GAAP. Accordingly, TVA will discontinue this regulatory accounting practice once all such deferred costs have been recovered, at which time it will recognize pension costs in accordance with U.S. GAAP. Cost Method. TVA uses the projected unit credit cost method to determine the service cost and the projected benefit obligation for retirement, termination, and ancillary benefits. Under this method, a "projected accrued benefit" is calculated at the beginning of the year and at the end of the year for each benefit that may be payable in the future. The "projected accrued benefit" is based on the plan's accrual formula and upon service at the beginning or end of the year, but it uses final average compensation, social security benefits, and other relevant factors projected to the age at which the employee is assumed to leave active service. The projected benefit obligation is the actuarial present value of the "projected accrued benefits" at the beginning of the year for employed participants and is the actuarial present value of all benefits for other participants. The service cost is the actuarial present value of the difference between the "projected accrued benefits" at the beginning and end of the year. Amortization of Net Gain or Loss. TVA utilizes the corridor approach for gain/loss amortization. Differences between actuarial assumptions and actual plan results are deferred and amortized into periodic cost only when the accumulated differences exceed 10 percent of the greater of the projected benefit obligation or the market-related value of plan assets. If necessary, the excess is amortized over the average remaining service period of participating employees expected to receive benefits. The current projected amortization periods of unrecognized net gain or loss is approximately 11 years for the pension plan and 12 years for the post-retirement plan. Amortization of Prior Service Cost/(Credit). Amortization of net prior service cost/(credit) resulting from a plan change is included as a component of period expense in the year first recognized and every year thereafter until it is fully amortized. The increase or decrease in the benefit obligation due to the plan change is amortized over the average remaining service period of participating employees expected to receive benefits under the plan. The pension and post-retirement plans have prior service costs/(credits) related to plan changes made in 2009, 2010, 2016, 2018, 2019, and 2020 with remaining amortization periods ranging from one to nine years. However, when a plan change reduces the benefit obligation, existing positive prior service costs are reduced or eliminated starting with the earliest established before a new prior service credit base is established.

Revenue (Policies)

Revenue (Policies)	12 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenues	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. Energy Prepayment Obligations In 2004, TVA and its largest customer, Memphis Light, Gas and Water Division ("MLGW"), entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 180 months. TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations. The arrangement ceased in 2019. Revenue was recognized in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as non-cash revenue on a cumulative basis during the life of the agreement, $10 million and $100 million of which was recognized as non-cash revenue during 2019 and 2018, respectively. Discounts to account for the time value of money, which are recorded as a reduction to electricity sales, amounted to $4 million and $46 million for the years ended September 30, 2019 and 2018, respectively.

Property, Plant, and Equipment

Property, Plant, and Equipment [Policy Text Block]	12 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Plant Retirement and Abandonment, Policy [Policy Text Block]	Financial Impact As a result of TVA's decision to accelerate the retirements of Paradise and Bull Run, certain construction projects at these locations were identified as probable of abandonment or were no longer expected to be in service for greater than one year prior to the plants' retirement dates. The write-off of these projects resulted in $11 million and $151 million of Operating and maintenance expense during the years ended September 30, 2020 and 2019, respectively. TVA also recognized losses of $2 million and $19 million in Operating and maintenance expense related to additional materials and supplies inventory reserves and write-offs identified at Paradise during the years ended September 30, 2020 and 2019, respectively. TVA's policy is to adjust depreciation rates to reflect the most current assumptions, ensuring units will be fully depreciated by the applicable retirement dates. As a result of TVA's decision to accelerate the retirement of Paradise and Bull Run, TVA recognized an additional $387 million and $566 million of accelerated depreciation for the years ended September 30, 2020 and 2019, respectively.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies [Table Text Block]	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Property, Plant, and Equipment Depreciation Rates	Average depreciation rates by asset class are as follows: Property, Plant, and Equipment Depreciation Rates At September 30 2020 2019 2018 Asset Class Nuclear 2.38 2.38 2.64 Coal-fired (1) 3.62 4.96 2.32 Hydroelectric 1.60 1.61 1.57 Gas and oil-fired 3.04 3.00 2.93 Transmission 1.34 1.34 1.32 Other 7.26 7.16 5.90

Accounts Receivable, Net Accoun

Accounts Receivable, Net Accounts Receivable, Net (Tables)	12 Months Ended
	Sep. 30, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
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 September 30 2020 2019 Power receivables $ 1,401 $ 1,624 Other receivables 128 115 Accounts receivable, net (1) $ 1,529 $ 1,739

Inventories, Net Inventories, N

Inventories, Net Inventories, Net (Tables)	12 Months Ended
	Sep. 30, 2020
Inventory, Net [Abstract]
Inventories, Net	The table below summarizes the types and amounts of TVA's inventories: Inventories, Net At September 30 2020 2019 Materials and supplies inventory $ 770 $ 742 Fuel inventory 253 294 RECs inventory, net 15 16 Allowance for inventory obsolescence (35) (53) Inventories, net $ 1,003 $ 999

Net Completed Plant Net Complet

Net Completed Plant Net Completed Plant (Tables)	12 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment, Net, by Type [Abstract]
Net Completed Plant	Net completed plant consisted of the following: Net Completed Plant At September 30 2020 2019 Cost Accumulated Depreciation Cost Accumulated Depreciation Net Coal-fired (1)(2) $ 18,613 $ 13,944 $ 4,669 $ 17,400 $ 12,538 $ 4,862 Gas and oil-fired 6,010 1,696 4,314 6,054 1,562 4,492 Nuclear 25,741 12,141 13,600 25,543 11,656 13,887 Transmission 8,283 3,140 5,143 7,932 3,083 4,849 Hydroelectric 3,410 1,090 2,320 3,163 1,051 2,112 Other electrical plant 1,981 1,146 835 1,920 1,110 810 Intangible software 3 2 1 3 1 2 Multipurpose dams 900 381 519 900 373 527 Other stewardship 29 10 19 29 10 19 Total $ 64,970 $ 33,550 $ 31,420 $ 62,944 $ 31,384 $ 31,560

Other Long-Term Assets Other Lo

Other Long-Term Assets Other Long-Term Assets (Tables)	12 Months Ended
	Sep. 30, 2020
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 September 30 2020 2019 (1) Loans and other long-term receivables, net $ 100 $ 125 EnergyRight ® receivables 69 81 Prepaid long-term service agreements 42 22 Commodity contract derivative assets 23 — Restricted cash and cash equivalents 21 23 Prepaid capacity payments 11 19 Other 59 55 Total other long-term assets $ 325 $ 325

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Sep. 30, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Components of regulatory assets and regulatory liabilities are summarized in the table below. Regulatory Assets and Liabilities At September 30 2020 2019 (1) Current regulatory assets Unrealized losses on interest rate derivatives $ 114 $ 89 Unrealized losses on commodity derivatives 4 39 Fuel cost adjustment receivable 12 28 Total current regulatory assets 130 156 Non-current regulatory assets Deferred pension costs and other post-retirement benefits costs 5,193 4,756 Non-nuclear decommissioning costs 2,512 1,741 Unrealized losses on interest rate derivatives 1,506 1,241 Nuclear decommissioning costs 896 868 Unrealized losses on commodity derivatives — 15 Other non-current regulatory assets 138 142 Total non-current regulatory assets 10,245 8,763 Total regulatory assets $ 10,375 $ 8,919 Current regulatory liabilities Fuel cost adjustment tax equivalents $ 115 $ 138 Unrealized gains on commodity derivatives 26 12 Total current regulatory liabilities 141 150 Non-current regulatory liabilities Unrealized gains on commodity derivatives 23 — Total non-current regulatory liabilities 23 — Total regulatory liabilities $ 164 $ 150

Other Long-Term Liabilities Oth

Other Long-Term Liabilities Other Long-Term Liabilities (Tables)	12 Months Ended
	Sep. 30, 2020
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 (1) At September 30 2020 2019 Interest rate swap liabilities $ 1,927 $ 1,676 Operating lease liabilities 171 — Currency swap liabilities 123 193 EnergyRight® financing obligation 78 90 Paradise pipeline financing obligation — 80 Accrued long-term service agreements 56 66 Other 193 203 Total other long-term liabilities $ 2,548 $ 2,308

Asset Retirement Obligations _2

Asset Retirement Obligations Asset Retirement Obligations (Tables)	12 Months Ended
	Sep. 30, 2020
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation Activity	Asset Retirement Obligation Activity Nuclear Non-Nuclear Total Balance at September 30, 2018 $ 2,989 $ 1,790 $ 4,779 Settlements (7) (82) (89) Revisions in estimate — 50 50 Additional obligations 18 — 18 Gallatin CCR — 672 672 Accretion (recorded as regulatory asset) 136 50 186 Balance at September 30, 2019 3,136 2,480 5,616 (1) Settlements (1) (113) (114) Revisions in estimate — 1,077 1,077 Accretion (recorded as regulatory asset) 143 63 206 Balance at September 30, 2020 $ 3,278 $ 3,507 $ 6,785 (1) Note (1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Debt and Other Obligations Debt

Debt and Other Obligations Debt and Other Obligations (Tables)	12 Months Ended
	Sep. 30, 2020
Debt and Other Obligations [Abstract]
Schedule of short-term borrowings	The following table provides information regarding TVA's short-term borrowings: Short-term Borrowings At September 30 2020 2019 2018 Gross amount outstanding - discount notes $ 57 $ 922 $ 1,217 Weighted average interest rate - discount notes 0.06 % 2.15 % 2.05 %
Debt Securities Activity	The table below summarizes the long-term debt securities activity for the years ended September 30, 2020 and 2019. Debt Securities Activity For the years ended September 30 2020 2019 Issues 2020 Series A (1) $ 1,000 $ — Discount on debt issues (3) — Total $ 997 $ — Redemptions/Maturities (2) electronotes ® $ 219 $ 5 2013 Series A 1,000 2009 Series B 28 30 2018 Series A 1,000 — 1999 Series A PARRS (TVE) 23 — 1998 Series D PARRS (TVC) 17 — 1995 Series B 140 — Total redemptions/maturities of power bonds 1,427 1,035 Notes payable 23 46 Variable interest entities 39 38 Total $ 1,489 $ 1,119 Notes (1) The 2020 Series A Bonds were issued at 99.7 percent of par. (2) All redemptions were at 100 percent of par.
Debt Outstanding	Total debt outstanding at September 30, 2020 and 2019, consisted of the following: Short-Term Debt CUSIP or Other Identifier Maturity Call/(Put) Date 2020 2019 Short-term debt, net of discounts $ 57 $ 922 Current maturities of long-term debt of VIEs issued at par 41 39 Current maturities of notes payable — 23 Current maturities of power bonds issued at par 880591EF5 12/15/2019 3.770% — 1 880591EF5 6/15/2020 3.770% — 27 880591EF5 12/15/2020 3.770% 1 — 880591EF5 6/15/2021 3.770% 28 — 88059TEL1 11/15/2019 2.650% — 1 88059TEL1 5/15/2020 2.650% — 1 880591EV0 3/15/2020 2.250% — 1,000 880591EL2 2/15/2021 3.875% 1,500 — 880591DC3 6/7/2021 5.805% 258 (1) — Total current maturities of power bonds issued at par 1,787 1,030 Total current debt outstanding, net $ 1,885 $ 2,014 Note (1) Includes net exchange gain from currency transactions of $73 million at September 30, 2020. Long-Term Debt At September 30 CUSIP or Other Identifier Maturity Coupon Effective Call Date 2020 Par 2019 Par Stock Exchange Listings electronotes ®(2) 5/15/2020 - 2/15/2043 2.375% - 3.625% 2/15/2015 - 2/15/2018 (5) $ — $ 217 None 880591EL2 2/15/2021 3.875% — 1,500 New York 880591DC3 6/7/2021 5.805% (3) — 246 (1) New York, Luxembourg 880591EN8 8/15/2022 1.875% 1,000 1,000 New York 880591ER9 9/15/2024 2.875% 1,000 1,000 New York 880591EW8 5/15/2025 0.750% 1,000 — New York 880591CJ9 11/1/2025 6.750% 1,350 1,350 New York, Hong Kong, Luxembourg, Singapore 880591EU2 2/1/2027 2.875% 1,000 1,000 New York 880591300 (4) 6/1/2028 2.134% 256 273 New York 880591409 (4) 5/1/2029 2.216% 208 232 New York 880591DM1 5/1/2030 7.125% 1,000 1,000 New York, Luxembourg 880591DP4 6/7/2032 6.587% (3) 323 (1) 307 (1) New York, Luxembourg 880591DV1 7/15/2033 4.700% 472 472 New York, Luxembourg 880591EF5 6/15/2034 3.770% 218 246 None 880591DX7 6/15/2035 4.650% 436 436 New York 880591CK6 4/1/2036 5.980% 121 121 New York 880591CS9 4/1/2036 5.880% 1,500 1,500 New York 880591CP5 1/15/2038 6.150% 1,000 1,000 New York 880591ED0 6/15/2038 5.500% 500 500 New York 880591EH1 9/15/2039 5.250% 2,000 2,000 New York 880591EP3 12/15/2042 3.500% 1,000 1,000 New York 880591DU3 6/7/2043 4.962% (3) 194 (1) 185 (1) New York, Luxembourg 880591CF7 7/15/2045 6.235% 7/15/2020 — 140 New York 880591EB4 1/15/2048 4.875% 500 500 New York, Luxembourg 880591DZ2 4/1/2056 5.375% 1,000 1,000 New York 880591EJ7 9/15/2060 4.625% 1,000 1,000 New York 880591ES7 9/15/2065 4.250% 1,000 1,000 New York Subtotal 18,078 19,225 Unamortized discounts, premiums, issue costs, and other (122) (131) Total long-term outstanding power bonds, net 17,956 19,094 Long-term debt of VIEs, net 1,048 1,089 Total long-term debt, net $ 19,004 $ 20,183 Notes (1) Includes net exchange gain from currency transactions of $80 million and $191 million at September 30, 2020 and 2019, respectively. (2) Includes one electronotes ® issue with partial maturities of principal for each required annual payment. (3) The coupon rate represents TVA's effective interest rate. (4) TVA PARRS, CUSIP numbers 880591300 and 880591409, may be redeemed under certain conditions. See Put and Call Options above.
Maturities Due in the Year Ending September 30	Maturities Due in the Year Ending September 30 2021 2022 2023 2024 2025 Thereafter Total Long-term power bonds, long-term debt of VIEs, and notes payable including current maturities (1) $ 1,901 $ 1,071 $ 69 $ 1,058 $ 1,059 $ 15,957 $ 21,115 Short-term debt, net of discounts 57 — — — — — 57 Note (1) Long-term power bonds does not include non-cash items of foreign currency exchange gain of $153 million, unamortized debt issue costs of $45 million, and net discount on sale of Bonds of $77 million. Long-term debt of VIE does not include non-cash item of unamortized debt issue costs of $8 million.
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 September 30, 2020 Maturity Date Facility Limit Letters of Credit Outstanding Cash Borrowings Availability December 2021 $ 150 $ 38 $ — $ 112 June 2023 1,000 432 — 568 September 2023 1,000 487 — 513 February 2025 500 500 — — Total $ 2,650 $ 1,457 $ — $ 1,193

Risk Management Activities an_2

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions (Tables)	12 Months Ended
	Sep. 30, 2020
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) For the years ended September 30 Derivatives in Cash Flow Hedging Relationship Objective of Hedge Transaction Accounting for Derivative 2020 2019 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 $ (1) $ (114) 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 For the years ended September 30 Derivatives in Cash Flow Hedging Relationship 2020 2019 Currency swaps $ 38 $ (45) 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 $27 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) For the years ended September 30 Derivative Type Objective of Derivative (2) Accounting for Derivative Instrument 2020 2019 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 $ (97) $ (79) 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 (1) — Notes (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 years ended September 30, 2020 and 2019.
Fair Values of TVA Derivatives	Fair Values of TVA Derivatives At September 30 2020 2019 Derivatives That Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Currency swaps £200 million Sterling $ (78) Accounts payable and accrued liabilities $(78) $ (90) Accounts payable and accrued liabilities $(6); Other long-term liabilities $(84) £250 million Sterling (63) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(58) (61) Accounts payable and accrued liabilities $(5); Other long-term liabilities $(56) £150 million Sterling (68) Accounts payable and accrued liabilities $(3); Other long-term liabilities $(65) (57) Accounts payable and accrued liabilities $(4); Other long-term liabilities $(53) Derivatives That Do Not Receive Hedge Accounting Treatment: Balance Balance Sheet Presentation Balance Balance Sheet Presentation Interest rate swaps $1.0 billion notional $ (1,449) Accounts payable and accrued liabilities $(43); Accrued interest $(37); Other long-term liabilities $(1,369) $ (1,261) Accounts payable and $476 million notional (588) Accounts payable and accrued liabilities $(22); Accrued interest $(10); Other long-term liabilities $(556) (498) Accounts payable and $42 million notional (4) Accounts payable and accrued liabilities $(2); Other long-term liabilities $(2) (5) Accounts payable and Commodity contract derivatives 46 Other current assets $26; Other long-term assets $23; Accounts payable and accrued liabilities $(3) (41) Other current assets $12; Other long-term liabilities $(16); Accounts payable and accrued liabilities $(37)
Currency Swaps Outstanding	TVA had the following currency swaps outstanding at September 30, 2020: Currency Swaps Outstanding September 30, 2020 Effective Date of Currency Swap Contract Associated TVA Bond Issues Currency Exposure Expiration Date of Swap Overall Effective 1999 £200 million 2021 5.81% 2001 £250 million 2032 6.59% 2003 £150 million 2043 4.96%
Commodity Contract Derivatives	Commodity Contract Derivatives At September 30 2020 2019 Number of Contracts Notional Amount Fair Value (MtM) Number of Contracts Notional Amount Fair Value ( MtM ) Coal contract derivatives — — million tons $ — 8 9 million tons $ (4) Natural gas contract derivatives 42 302 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 September 30, 2020 and 2019, are shown in the table below. Derivative Assets and Liabilities (1) (in millions) At September 30, 2020 At September 30, 2019 Assets Commodity derivatives not subject to master netting or similar arrangement $ 49 $ 12 Liabilities Currency swaps (2) $ 209 $ 208 Interest rate swaps (2) 2,041 1,764 Total derivatives subject to master netting or similar arrangement 2,250 1,972 Commodity derivatives not subject to master netting or similar arrangement 3 53 Total liabilities $ 2,253 $ 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 September 30, 2020 or 2019.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 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) At or for the years ended September 30 Fund Financial Statement Presentation 2020 2019 NDT Regulatory asset $ 37 $ (112) ART Regulatory asset 32 (70) SERP Other income (expense) 3 — DCP Other income (expense) 2 (2)
Fair Value Measurements		Fair Value Measurements At September 30, 2020 Quoted Prices in Active Significant Other Significant Total Assets Investments Equity securities $ 500 $ — $ — $ 500 Government debt securities (1) 485 40 — 525 Corporate debt securities (2) — 356 — 356 Mortgage and asset-backed securities — 27 — 27 Institutional mutual funds 188 — — 188 Forward debt securities contracts — 13 — 13 Private equity funds measured at net asset value (3) — — — 194 Private real asset funds measured at net asset value (3) — — — 168 Private credit measured at net asset value (3) — — — 53 Commingled funds measured at net asset value (3) — — — 1,174 Total investments 1,173 436 — 3,198 Commodity contract derivatives — 49 — 49 Total $ 1,173 $ 485 $ — $ 3,247 Quoted Prices in Active Markets for Identical Liabilities Significant Other Significant Total Liabilities Currency swaps (4) $ — $ 209 $ — $ 209 Interest rate swaps — 2,041 — 2,041 Commodity contract derivatives — 3 — 3 Total $ — $ 2,253 $ — $ 2,253 Notes (1) Includes government-sponsored entities. (2) Includes both U.S. and foreign debt. (3) 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. (4) 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 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities . Fair Value Measurements At September 30, 2019 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 asset 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 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 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities .
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 Balance at October 1, 2018 $ 58 Change in net unrealized gains (losses) deferred as regulatory assets and liabilities (62) Balance at September 30, 2019 (4) Settlements (1) Change in net unrealized gains (losses) deferred as regulatory assets and liabilities 5 Balance at September 30, 2020 $ —
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 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 September 30, 2020 and 2019, were as follows: Estimated Values of Financial Instruments Not Recorded at Fair Value At September 30, 2020 At September 30, 2019 Valuation Classification Carrying Fair Carrying Fair EnergyRight ® receivables (including current portion) Level 2 $ 87 $ 86 $ 101 $ 100 Loans and other long-term receivables, net (including current portion) Level 2 $ 105 $ 93 $ 131 $ 120 EnergyRight ® financing obligations (including current portion) Level 2 $ 97 $ 108 $ 113 $ 126 Unfunded loan commitments Level 2 $ — $ 2 $ — $ 10 Membership interests of VIEs subject to mandatory redemption (including current portion) Level 2 $ 26 $ 35 $ 28 $ 37 Long-term outstanding power bonds (including current maturities), net Level 2 $ 19,743 $ 26,630 $ 20,124 $ 26,059 Long-term debt of VIEs (including current maturities), net Level 2 $ 1,089 $ 1,419 $ 1,128 $ 1,371 Long-term notes payable (including current maturities) Level 2 $ — $ — $ 23 $ 23

Proprietary Capital (Tables)

Proprietary Capital (Tables)	12 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	Accumulated Other Comprehensive Income (Loss) The items included in AOCI consist of market valuation adjustments for certain derivative instruments. See Note 15 — Risk Management Activities and Derivative Transactions .
Stockholders' Equity Note [Abstract]
Summary of Proprietary Capital Activity	The table below summarizes TVA's activities related to appropriated funds and retained earnings. Summary of Proprietary Capital Activity At or for the years ended September 30 2020 2019 Power Program Nonpower Power Program Nonpower Appropriation Investment $ 258 $ 4,351 $ 258 $ 4,351 Proprietary Capital Balance at beginning of year 10,823 (3,795) 9,404 (3,787) Net income (loss) for year 1,360 (8) 1,425 (8) Return on power program appropriation investment (6) — (6) — Balance at end of year 12,177 (3,803) 10,823 (3,795) Net proprietary capital at September 30 $ 12,435 $ 548 $ 11,081 $ 556

Other Income (Expense), Net Oth

Other Income (Expense), Net Other Income (Expense), Net (Tables)	12 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Other Income (Expense), Net	Income and expenses not related to TVA's operating activities are summarized in the following table: Other Income (Expense), Net For the years ended September 30 2020 2019 2018 Bellefonte deposit $ — $ 21 $ — Interest income 18 25 23 External services 12 13 14 Gains (losses) on investments 9 3 6 Miscellaneous (3) — 7 Total other income (expense), net $ 36 $ 62 $ 50

Benefit Plans Benefit Plans (Ta

Benefit Plans Benefit Plans (Tables)	12 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Obligations and Funded Status	The changes in plan obligations, assets, and funded status for the years ended September 30, 2020 and 2019, were as follows: Obligations and Funded Status For the years ended September 30 795,900,000 Pension Benefits Other Post-Retirement Benefits 2020 2019 2020 2019 Change in benefit obligation Benefit obligation at beginning of year $ 13,312 $ 11,725 $ 499 $ 428 Service cost 55 44 16 11 Interest cost 415 499 16 18 Plan participants' contributions 6 7 — — Collections (1) — — 20 22 Actuarial (gain) loss 614 1,756 39 78 Plan change 2 7 — — Net transfers (to) from variable fund/401(k) plan 2 1 — — Expenses paid (5) (6) — — Benefits paid (726) (721) (46) (58) Benefit obligation at end of year 13,675 13,312 544 499 Change in plan assets Fair value of net plan assets at beginning of year 7,980 8,003 — — Actual return on plan assets 397 389 — — Plan participants' contributions 6 7 — — Collections (1) — — 20 22 Net transfers (to) from variable fund/401(k) plan 2 1 — — Employer contributions 305 307 26 36 Expenses paid (5) (6) — — Benefits paid (726) (721) (46) (58) Fair value of net plan assets at end of year 7,959 7,980 — — Funded status $ (5,716) $ (5,332) $ (544) $ (499) Note (1) Collections include retiree contributions as well as provider discounts and rebates.
Amounts Recognized on TVA's Consolidated Balance Sheets	Amounts related to these benefit plans recognized on TVA's Consolidated Balance Sheets consist of regulatory assets and liabilities that have not been recognized as components of net periodic benefit cost at September 30, 2020 and 2019, and the funded status of TVA's benefit plans, which are included in Accounts payable and accrued liabilities and Post-retirement and post-employment benefit obligations: Amounts Recognized on TVA's Consolidated Balance Sheets At September 30 Pension Benefits Other Post-Retirement Benefits 2020 2019 2020 2019 Regulatory assets (liabilities) $ 5,115 $ 4,731 $ 78 $ 25 Accounts payable and accrued liabilities (5) (5) (28) (28) Pension and post-retirement benefit obligations (1) (5,711) (5,327) (516) (471) Note (1) The table above excludes $390 million and $383 million of post-employment benefit costs that are recorded in Post-retirement and post-employment benefit obligations on the Consolidated Balance Sheets at September 30, 2020 and 2019, respectively.
Post-Retirement Benefit Costs Deferred as Regulatory Assets	Unrecognized amounts included in regulatory assets or liabilities yet to be recognized as components of accrued benefit cost at September 30, 2020 and 2019, consisted of the following: Post-Retirement Benefit Costs Deferred as Regulatory Assets (Liabilities) At September 30 Pension Benefits Other Post-Retirement Benefits 2020 2019 2020 2019 Unrecognized prior service credit $ (615) $ (714) $ (112) $ (135) Unrecognized net loss 5,620 5,350 190 160 Amount capitalized due to actions of regulator 110 95 — — Total regulatory assets (liabilities) $ 5,115 $ 4,731 $ 78 $ 25
Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets	The projected benefit obligation, accumulated benefit obligation, and fair value of plan assets for the pension plan at September 30, 2020 and 2019, were as follows: Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets At September 30 2020 2019 Projected benefit obligation $ 13,675 $ 13,312 Accumulated benefit obligation 13,613 13,246 Fair value of net plan assets 7,959 7,980
Components of Net Periodic Benefit Cost	The components of net periodic benefit cost and other amounts recognized as changes in regulatory assets for the years ended September 30, 2020, 2019, and 2018 were as follows: Components of Net Periodic Benefit Cost For the years ended September 30 Pension Benefits Other Post-Retirement Benefits 2020 2019 2018 2020 2019 2018 Service cost $ 55 $ 44 $ 53 $ 16 $ 11 $ 14 Interest cost 415 499 473 16 18 19 Expected return on plan assets (488) (477) (478) — — — Amortization of prior service credit (97) (99) (99) (24) (24) (22) Recognized net actuarial loss 436 336 409 10 4 8 Total net periodic benefit cost as actuarially determined 321 303 358 18 9 19 Amount expensed (capitalized) due to actions of regulator (15) 1 (54) — — — Net periodic benefit cost $ 306 $ 304 $ 304 $ 18 $ 9 $ 19
Expected Amortization of Regulatory Assets in Next Fiscal Year	The amounts in the regulatory asset that are expected to be recognized as components of net periodic benefit cost during the next fiscal year are as follows: Expected Amortization of Regulatory Assets in 2021 At September 30, 2020 Pension Benefits Other Post-Retirement Total Prior service credit $ (97) $ (18) $ (115) Net actuarial loss 447 12 459 Amounts expensed due to actions of regulator 28 — 28
Actuarial Assumptions	Actuarial Assumptions Utilized to Determine Benefit Obligations at September 30 Pension Benefits Other Post-Retirement Benefits 2020 2019 2020 2019 Discount rate 2.75% 3.20% 3.05% 3.30% Rate of compensation increase 3.43% 3.50% N/A N/A Cost of living adjustment (COLA) (1) 2.00% 2.00% 2.00% 2.00% Pre-Medicare eligible Current health care cost trend rate (2) N/A N/A 6.50% 6.75% Ultimate health care cost trend rate N/A N/A 5.00% 5.00% Year ultimate trend rate is reached N/A N/A 2027 2027 Post-Medicare eligible Current health care cost trend rate N/A N/A —% —% Ultimate health care cost trend rate N/A N/A 4.00% 4.00% Year ultimate trend rate is reached N/A N/A 2024 2023 Notes (1) The COLA assumption is the ultimate long-term rate. The calendar year rate for 2021 is assumed to be one percent, and for years thereafter the ultimate is used. (2) In 2019, TVA reset the pre-Medicare health care cost trend rates assumption with an initial rate of 6.75 percent, declining 0.25 percent per year until it reaches the ultimate rate of 5.00 percent in 2027. For 2020, TVA maintained this trend assumption for pre-Medicare per capita claims cost with a current health care cost rate of 6.50 percent. However, to account for cumulative delayed medical care due to the COVID-19 pandemic and the expected spending as the demand for care returns, the pre-Medicare per capita retiree contributions current health care cost trend rate is 11.93 percent, and in 2022 assumed to return to 6.25 percent in line with the health care cost trend rates assumption. Actuarial Assumptions Utilized to Determine Net Periodic Benefit Cost for the Years Ended September 30 (1) Pension Benefits Other Post-Retirement Benefits 2020 2019 2018 2020 2019 2018 Discount rate 3.20 % 4.35 % 3.85 % 3.30 % 4.40 % 3.95 % Expected return on plan assets (2) 6.75 % 6.75 % 6.75 % N/A N/A N/A Cost of living adjustment (COLA) (3) 2.00 % 2.00 % 2.00 % 2.00 % 2.00 % 2.00 % Rate of compensation increase 3.43 % 3.50 % 5.34 % N/A N/A N/A Pre-Medicare eligible Current health care cost trend rate N/A N/A N/A 6.75 % 6.25 % 6.50 % Ultimate health care cost trend rate N/A N/A N/A 5.00 % 5.00 % 5.00 % Year ultimate trend rate is reached N/A N/A N/A 2027 2024 2024 Post-Medicare eligible Current health care cost trend rate N/A N/A N/A — % — % — % Ultimate health care cost trend rate N/A N/A N/A 4.00 % 4.00 % 4.00 % Year ultimate trend rate is reached N/A N/A N/A 2023 2021 2021 Notes (1) The actuarial assumptions used to determine the benefit obligations at September 30 of each year are subsequently used to determine net periodic benefit cost for the following year except the rate of compensation increase assumption. (2) The actual return on assets for 2020, 2019, and 2018 were 5.11%, 4.99%, and 5.84%, respectively. (3) The COLA assumption is the ultimate rate. The actual calendar year rate is used in determining the expense, and for years thereafter the ultimate rate is used.
Sensitivity to Certain Changes in Pension Assumptions	The following chart reflects the sensitivity of pension cost to changes in certain actuarial assumptions: Sensitivity to Certain Changes in Pension Assumptions At September 30, 2020 Actuarial Assumption Change in Assumption Impact on 2020 Pension Cost Impact on 2020 Projected Benefit Obligation Discount rate (0.25) % $ 17 $ 418 Rate of return on plan assets (0.25) % 18 N/A Cost of living adjustments 0.25 % 30 270
Sensitivity to Changes in Assumed Health Care Cost Trend Rates	The following chart reflects the sensitivity of post-retirement benefit cost to changes in the health care trend rate: Sensitivity to Changes in Assumed Health Care Cost Trend Rates At September 30, 2020 1% Increase 1% Decrease Effect on total of service and interest cost components for the year $ 4 $ (4) Effect on end-of-year accumulated post-retirement benefit obligation 70 (68)
Asset Holdings and Fair Value Measurements	s consistent with the asset allocation policy. At September 30, 2020 and 2019, the asset holdings of TVARS included the following: Asset Holdings of TVARS At September 30 Plan Assets at September 30 Asset Category Target Allocation 2020 2019 Global public equity 32 % 36 % 37 % Private equity 8 % 13 % 10 % Safety oriented fixed income 20 % 18 % 18 % Opportunistic fixed income 20 % 15 % 12 % Public real assets 10 % 10 % 15 % Private real assets 10 % 8 % 8 % Total 100 % 100 % 100 % Fair Value Measurements The following table provides the fair value measurement amounts for assets held by TVARS at September 30, 2020: TVA Retirement System At September 30, 2020 Total (1)(2) Quoted Prices in Active Markets for Identical Significant Other Significant Assets Equity securities $ 1,624 $ 1,621 $ — $ 3 Preferred securities 11 — 11 — Debt securities Corporate debt securities 1,421 — 1,418 3 Residential mortgage-backed securities 317 — 314 3 Debt securities issued by U.S. Treasury 701 701 — — Debt securities issued by foreign governments 231 — 179 52 Asset-backed securities 116 — 88 28 Debt securities issued by state/local governments 23 — 23 — Commercial mortgage-backed securities 91 — 86 5 Commingled funds measured at net asset value (3) Equity 931 — — — Debt 203 — — — Blended 102 — — — Institutional mutual funds 277 277 — — Cash equivalents and other short-term investments 338 77 261 — Private credit measured at net asset value (3) 166 — — — Private equity measured at net asset value (3) 1,003 — — — Private real assets measured at net asset value (3) 629 — — — Securities lending collateral 167 — 167 — Derivatives Futures 3 3 — — Swaps 10 — 10 — Options 2 — 2 — Foreign currency forward receivable 2 — 2 — Total assets $ 8,368 $ 2,679 $ 2,561 $ 94 Liabilities Derivatives Futures $ 1 $ 1 $ — $ — Foreign currency forward payable 3 — 3 — Swaps 6 — 6 — Options 2 — 2 — Securities sold under agreements to repurchase 123 — 123 — Total liabilities $ 135 $ 1 $ 134 $ — Notes (1) Excludes approximately $107 million in net payables associated with security purchases and sales and various other payables. (2) Excludes a $167 million payable for collateral on loaned securities in connection with TVARS's participation in securities lending programs. (3) In accordance with Subtopic 820-10, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The following table provides the fair value measurement amounts for assets held by TVARS at September 30, 2019: TVA Retirement System At September 30, 2019 Total (1)(2) Quoted Prices in Active Markets for Identical Significant Other Significant Assets Equity securities $ 1,766 $ 1,762 $ — $ 4 Preferred securities 10 1 9 — Debt securities Corporate debt securities 1,387 — 1,382 5 Residential mortgage-backed securities 427 — 424 3 Debt securities issued by U.S. Treasury 807 807 — — Debt securities issued by foreign governments 210 — 209 1 Asset-backed securities 144 — 116 28 Debt securities issued by state/local governments 18 — 18 — Commercial mortgage-backed securities 81 — 80 1 Commingled funds measured at net asset value (3) Equity 795 — — — Debt 308 — — — Commodities 217 — — — Blended 125 — — — Institutional mutual funds 97 97 — — Cash equivalents and other short-term investments 329 1 328 — Certificates of deposit 3 — 3 — Private credit measured at net asset value (3) 78 — — — Private equity measured at net asset value (3) 778 — — — Private real assets measured at net asset value (3) 659 — — — Securities lending collateral 224 — 224 — Derivatives Futures 2 2 — — Swaps 5 — 5 — Options 1 — 1 — Foreign currency forward receivable 1 — 1 — Total assets $ 8,472 $ 2,670 $ 2,800 $ 42 Liabilities Derivatives Futures $ 4 $ 4 $ — $ — Foreign currency forward payable 1 — 1 — Swaps 12 — 12 — Options 1 — 1 — Securities sold under agreements to repurchase 118 — 118 — Total liabilities $ 136 $ 4 $ 132 $ — cNotes (1) Excludes approximately $132 million in net payables associated with security purchases and sales and various other payables. (2) Excludes a $224 million payable for collateral on loaned securities in connection with TVARS's participation in securities lending programs.
Fair Value Measurements Using Significant Unobservable Inputs	The following table provides a reconciliation of beginning and ending balances of pension plan assets measured at fair value on a recurring basis where the determination of fair value includes significant unobservable inputs (Level 3): Fair Value Measurements Using Significant Unobservable Inputs Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Balance at October 1, 2018 $ 58 Net realized/unrealized gains (losses) 4 Purchases, sales, issuances, and settlements (net) (12) Transfers in and/or out of Level 3 (8) Balance at September 30, 2019 42 Net realized/unrealized gains (losses) 46 Purchases, sales, issuances, and settlements (net) 11 Transfers in and/or out of Level 3 (5) Balance at September 30, 2020 $ 94
Estimated Future Benefit Payments	Cash Flows Estimated Future Benefit Payments. The following table sets forth the estimated future benefit payments under the benefit plans. Estimated Future Benefits Payments At September 30, 2020 Pension Benefits (1) Other Post-Retirement Benefits 2021 $ 777 $ 28 2022 776 26 2023 773 24 2024 768 23 2025 767 22 2026 - 2030 3,741 117 Note (1) Participants are assumed to receive the Fixed Fund in a lump sum in lieu of available annuity options allowed for certain grandfathered participants resulting in higher estimated pension benefits payments.
Amounts recognized on Consolidated Balance Sheets	Amounts Recognized on TVA's Consolidated Balance Sheets At September 30 2020 2019 Accounts payable and accrued liabilities $ — $ 36 Post-retirement and post-employment benefit obligations 390 383

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of lease/leaseback future minimum payments [Table Text Block]	At September 30, 2020, the future minimum payments under leaseback obligations are shown below. Lease/Leasebacks Minimum payments due in years ending September 30 2021 $ 207 2022 25 2023 — 2024 — 2025 — Thereafter — Total $ 232
Schedule of future minimum payments for membership interests subject to mandatory redemption [Table Text Block]	At September 30, 2020, the mandatory redemptions for each of the next five years are shown below: 2021 2022 2023 2024 2025 Membership interests of variable interest entity subject to mandatory redemption $ 3 $ 3 $ 2 $ 1 $ 1
Energy Prepayment Obligations	In addition to the commitments above, TVA had contractual obligations in the form of revenue discounts related to energy prepayments. TVA recognized $10 million of prepayment obligations and related interest payments of $4 million in revenue during 2019. The arrangement ceased in 2019. See Note 1 — Summary of Significant Accounting Policies — Energy Prepayment Obligations and Note 17 — Revenue .
Unfunded loan commitments	At September 30, 2020, TVA's commitments under unfunded loan commitments were $1 million for 2021. TVA has no commitments under unfunded loan commitments for 2022 through 2025.

Related Parties Related Parties

Related Parties Related Parties (Tables)	12 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Transactions with agencies of the federal government were as follows: Related Party Transactions For the years ended, or at, September 30 2020 2019 2018 Revenue from sales of electricity $ 105 $ 118 $ 122 Other income 260 258 240 Expenditures Operating expenses 224 222 220 Additions to property, plant, and equipment 9 10 8 Cash and cash equivalents 31 45 46 Accounts receivable, net 94 76 60 Investment funds 485 279 199 Long-term accounts receivable 27 53 46 Accounts payable and accrued liabilities 39 69 69 Long-term power bonds, net 1 — — Return on power program appropriation investment 6 6 5

Unaudited Quarterly Financial_2

Unaudited Quarterly Financial Information Unaudited Quarterly Financial Information (Tables)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Financial Information	Unaudited Quarterly Financial Information 2020 First Second Third Fourth Total Operating revenues $ 2,578 $ 2,521 $ 2,251 $ 2,899 $ 10,249 Operating expenses 2,046 1,914 1,716 1,862 7,538 Operating income 532 607 535 1,037 2,711 Net income (loss) 192 255 205 700 1,352 Unaudited Quarterly Financial Information 2019 First Second Third Fourth Total Operating revenues $ 2,725 $ 2,750 $ 2,604 $ 3,239 $ 11,318 Operating expenses 1,960 2,158 2,088 2,301 8,507 Operating income 765 592 516 938 2,811 Net income (loss) 423 241 165 588 1,417

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue Recognition, Incentives [Policy Text Block]	Economic Development Incentives. Under certain economic development programs TVA offers incentives to existing and potential power customers in targeted business sectors that make multi-year commitments to invest in the Tennessee Valley. TVA records those incentives as reductions of revenue. In 2020 and 2019, TVA recorded a total of $318 million and $310 million, respectively, in incentives as a reduction of revenue. 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 September 30, 2020 and 2019, the outstanding unpaid incentives were $172 million and $157 million, respectively. Incentives that have been paid out may be subject to claw back if the customer fails to meet certain program requirements. Additionally, in May 2020, TVA established flexibility provisions to support the continued operations and recovery of participating customers experiencing financial and operational hardships as a result of the COVID-19 pandemic and corresponding economic downturn. These provisions have not had a material impact to TVA.
Revenues	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. Energy Prepayment Obligations In 2004, TVA and its largest customer, Memphis Light, Gas and Water Division ("MLGW"), entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 180 months. TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations. The arrangement ceased in 2019. Revenue was recognized in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as non-cash revenue on a cumulative basis during the life of the agreement, $10 million and $100 million of which was recognized as non-cash revenue during 2019 and 2018, respectively. Discounts to account for the time value of money, which are recorded as a reduction to electricity sales, amounted to $4 million and $46 million for the years ended September 30, 2019 and 2018, respectively.
Disaggregation of Revenue [Table Text Block]	Disaggregated Revenue In 2020, the revenues generated from TVA's electricity sales were $10.1 billion and accounted for virtually all of TVA's revenues. TVA's revenues by state for each of the last three years are detailed in the table below: Operating Revenues By State For the years ended September 30 (in millions) 2020 2019 2018 Alabama $ 1,439 $ 1,593 $ 1,600 Georgia 249 270 267 Kentucky 624 691 696 Mississippi 941 1,063 1,052 North Carolina 65 74 66 Tennessee 6,740 7,419 7,350 Virginia 42 45 48 Subtotal 10,100 11,155 11,079 Off-system sales 4 4 7 Revenue capitalized during pre-commercial plant operations (1) — — (11) Revenue from sales of electricity 10,104 11,159 11,075 Other revenue 145 159 158 Total operating revenues $ 10,249 $ 11,318 $ 11,233 Note (1) Represents revenue capitalized during pre-commercial operations of $11 million at Allen CC in 2018. See Note 1 — Summary of Significant Accounting Policies — Pre-Commercial Plant Operations . TVA's operating revenues by customer type for each of the last three years are detailed in the table below: Operating Revenues by Customer Type For the years ended September 30 (in millions) 2020 2019 2018 Revenue from sales of electricity Local power companies (1) $ 9,406 $ 10,351 $ 10,262 Industries directly served 588 686 695 Federal agencies and other 110 122 129 Revenue capitalized during pre-commercial plant operations (2) — — (11) Revenue from sales of electricity 10,104 11,159 11,075 Other revenue 145 159 158 Total operating revenues $ 10,249 $ 11,318 $ 11,233 Notes (1) The amount for the years ended September 30, 2020 and 2019, is net of $163 million and $14 million, respectively, of wholesale bill credits to LPCs participating in the long-term Partnership Agreement. There were no such credits in 2018. (2) Represents revenue capitalized during pre-commercial operations of $11 million at Allen CC in 2018. See Note 1 — Summary of Significant Accounting Policies — Pre-Commercial Plant Operations . TVA and LPCs continue to work together to meet the changing needs of consumers around the Tennessee Valley. In 2019, 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 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 June 2020, TVA provided participating LPCs a flexibility option that allows them to locally generate up to approximately five percent of average total hourly energy sales over the prior five years in order to meet their individual customers' needs. As of November 16, 2020, 142 LPCs had signed the 20-year Partnership Agreement with TVA, and 64 LPCs had signed a Flexibility Agreement. In August 2020, the TVA Board approved a $200 million Pandemic Relief Credit. The 2.5 percent base rate credit will be applied beginning in October 2020 and will remain in effect through the end of 2021. The credit will apply to service provided to TVA's local power company customers, their large commercial and industrial customers, and TVA directly served customers. The number of LPCs with the contract arrangements described below, the revenues derived from such arrangements during 2020, and the percentage of TVA's total operating revenues during 2020 represented by these revenues are summarized in the tables below: TVA Local Power Company Contracts At or for the year ended September 30, 2020 Contract Arrangements (1) Number of LPCs Revenue from Sales of Electricity to LPCs Percentage of Total Operating Revenues 20-year termination notice 142 $ 7,666 74.8 % 5-year termination notice 11 1,740 17.0 % Total (2) 153 $ 9,406 91.8 % Notes (1) Ordinarily, the LPCs and TVA have the same termination notice period; however, in contracts with two 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. (2) TVA wholesale power contracts decreased to 153 in 2020 due to a merger between two LPCs in July 2020. TVA's two largest LPCs — MLGW and NES — have contracts with a five-year and a 20-year termination notice period, respectively. Sales to MLGW and NES accounted for nine percent and eight percent, respectively, of TVA's total operating revenues in 2020. In May 2020, MLGW published a draft IRP to guide energy choices in the future, and in July 2020, TVA made a proposal to MLGW that highlights the benefits of remaining a TVA customer. In August 2020, MLGW published a final IRP and announced its plan to issue requests for proposal to validate the cost estimates included in the IRP. In addition, certain other LPCs are evaluating options for future energy choices.
Contract with Customer, Asset and Liability [Table Text Block]	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 as of September 30, 2020. 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.
Energy Prepayment Obligation [Table Text Block]	Energy Prepayment Obligations. In 2004, TVA and its largest customer, MLGW, entered into an energy prepayment agreement under which MLGW prepaid TVA $1.5 billion for the future costs of electricity to be delivered by TVA to MLGW over a period of 15 years.  TVA accounted for the prepayment as unearned revenue and reported the obligation to deliver power under this arrangement as Energy prepayment obligations.  The arrangement ceased in 2019. TVA recognized approximately $100 million of noncash revenue in each year of the arrangement as electricity was delivered to MLGW based on the ratio of units of kilowatt hours delivered to total units of kilowatt hours under contract. As of September 30, 2019, $1.5 billion had been recognized as noncash revenue on a cumulative basis during the life of the agreement, $100 million of which was recognized as noncash revenue and a corresponding reduction in the balance of Energy prepayment obligations during 2018. During 2019, $10 million was recognized as noncash revenue and a corresponding reduction in the balance of Energy prepayment obligations. Discounts to account for the time value of money, which were recorded as a reduction to electricity sales, amounted to $4 million and $46 million during 2019 and 2018, respectively.

Leases (Table Text Block)

Leases (Table Text Block)	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Amounts Recognized on Balance Sheets	The following table provides additional information regarding the presentation of leases on the Consolidated Balance Sheets at September 30, 2020 : Amounts Recognized on TVA's Consolidated Balance Sheets At September 30, 2020 Assets Operating Operating lease assets, net of amortization $ 232 Finance Finance leases 516 Total lease assets $ 748 Liabilities Current Operating Accounts payable and accrued liabilities $ 63 Finance Accounts payable and accrued liabilities 41 Non-current Operating Other long-term liabilities 171 Finance Finance lease liabilities 525 Total lease liabilities $ 800
Lease Costs	TVA's leases consist primarily of railcars, equipment, real estate/land, power generating facilities, and gas pipelines. TVA's leases have various terms and expiration dates remaining from less than one year to 26 years. The components of lease costs for the year September 30, 2020, were as follows: Lease Costs For the year ended September 30, 2020 Operating lease costs (1) $ 84 Variable lease costs (1) 75 Short-term lease costs (1) 7 Finance lease costs Amortization of lease assets (2) 15 Interest on lease liabilities (3)(4) 33 Total finance lease costs 48 Total lease costs $ 214 Notes (1) Costs are included in Operating and maintenance expense, Fuel expense, Purchased power expense, and Tax equivalents expense on the Consolidated Statements of Operations. TVA's rental expense for operating leases was approximately $97 million and $92 million for the years ended September 30, 2019 and 2018, respectively. (2) Expense is included in Depreciation and amortization expense on the Consolidated Statements of Operations. (3) Expense is included in Interest expense on the Consolidated Statements of Operations. (4) Certain finance leases receive regulatory accounting treatment and are reclassified to Fuel expense and Purchased power expense.
Amounts Recognized on Statements of Cash Flows	The following table contains additional information with respect to cash and non-cash activities related to leases: Amounts Recognized on TVA's Consolidated Statements of Cash Flows For the Year Ended September 30, 2020 Operating cash flows for operating leases $ 85 Operating cash flows for finance leases 33 Financing cash flows for finance leases 15 Lease assets obtained in exchange for lease obligations (non-cash) Operating leases (1) $ 110 Finance leases 394 Note (1) Amount excludes operating lease assets recorded as a result of the adoption of the new lease standard.
Weighted Averages	TVA has certain finance leases under PPAs under which the present value of the minimum lease payments exceeds the fair value of the related lease asset at the date of measurement. This resulted in an interest rate that was higher than TVA's incremental borrowing rate. At September 30, 2020 , the weighted average remaining lease term in years and the weighted average discount rate for TVA's operating and financing leases were as follows: Weighted Averages At September 30, 2020 Weighted average remaining lease terms Operating leases 5 years Finance leases 12 years Weighted average discount rate (1) Operating leases 1.6% Finance leases 21.8% Note (1) The discount rate is calculated using the rate implicit in a lease if it is readily determinable. If the rate used by the lessor is not readily determinable, TVA uses its incremental borrowing rate as permitted by accounting guidance. The incremental borrowing rate is influenced by TVA's credit rating and lease term and as such may differ for individual leases, embedded leases, or portfolios of leased assets.
Future Minimum Lease Payments	The following table presents maturities of lease liabilities and a reconciliation of the undiscounted cash flows to lease liabilities at September 30, 2020 : Future Minimum Lease Payments Minimum Payments Due at September 30, 2020 Operating leases 2021 $ 66 2022 51 2023 39 2024 37 2025 34 Thereafter 16 Minimum annual payments 243 Less: present value discount (9) Operating present value of net minimum lease payments $ 234 Finance leases 2021 $ 92 2022 93 2023 92 2024 87 2025 86 Thereafter 592 Minimum annual payments 1,042 Less: amount representing interest (476) Finance present value of net minimum lease payments $ 566

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - General (Details) People in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)People	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2015USD ($)
Accounting Policies [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 500	$ 299
Allowance for uncollectible accounts - loans		1
Revenue Capitalized During Pre-Commercial Operations	0	0	$ 11
Fuel Cost Capitalized During Pre-Commercial Operations		19
Recorded cost for emission allowances granted by the Environmental Protection Agency	0
Reimbursements from DOE	89
Restricted Cash and Investments, Noncurrent	21	23
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	521	322	$ 322	$ 311
Accounts receivable from DOE	6
Appropriation-investment power program	$ 258	258			$ 1,000
Population of Service Area [Line Items]
Population of service area | People	10
Total
Accounting Policies [Abstract]
Discounts reducing electricity sales	$ 4	46
MLGW
Accounting Policies [Abstract]
Deferred revenue, revenue recognized		$ 100

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reclassificatons (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Reclassifications
Finance Lease, Liability	$ 525	$ 182

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Portion at Other than Fair Value Measurement [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, after Allowance for Credit Loss	$ 105	$ 131
Financing Receivable, after Allowance for Credit Loss	$ 93	120
Period of time for customers to fulfill payment arrangements	90 days
Allowance for uncollectible accounts - receivables		1
Allowance for uncollectible accounts - loans		1
Fuel Cost Capitalized During Pre-Commercial Operations		$ 19

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Property, Plant, and Equipment, and Depreciation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Property, Plant, and Equipment, and Depreciation
Depreciation	$ 1,600	$ 1,800	$ 1,300
Composite depreciation rate for completed plant	2.74%	3.09%	2.45%
Accelerated depreciation		$ 566	$ 48
Reacquired Rights	$ 192	200
Amortization of Reacquired Rights	$ 8	8	8
Capitalized software amortization period	seven years
Unamortized computer software costs	$ 54	63
Amortization expense of capitalized computer software costs	$ 42	$ 38	$ 32
Nuclear
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	2.38%	2.38%	2.64%
Coal-fired
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	3.62%	4.96%	2.32%
Hydroelectric
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	1.60%	1.61%	1.57%
Gas and oil-fired
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	3.04%	3.00%	2.93%
Transmission
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	1.34%	1.34%	1.32%
Other
Property, Plant, and Equipment, and Depreciation
Composite depreciation rate for completed plant	7.26%	7.16%	5.90%

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Energy Prepayment Obligations and Discounts on Sales (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2004
Energy Prepayment Obligations and Discounts on Sales
Accounts Receivable, Allowance for Credit Loss, Current		$ 1
MLGW prepayment				$ 1,500
MLGW prepayment period				180 months
Recognition of Deferred Revenue	$ 0	$ 10	$ 100
MLGW
Energy Prepayment Obligations and Discounts on Sales
Recognition of Deferred Revenue	$ 1,500
Deferred revenue expected recognition each year	10 million	100 million		100 million
Deferred revenue, revenue recognized		$ 100
Total
Energy Prepayment Obligations and Discounts on Sales
Discounts reducing electricity sales	$ 4	$ 46

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Leases (Details) $ in Millions	Sep. 30, 2020USD ($)
Leases
Finance lease under PPA	$ 500
Operating lease under PPA	$ 174

Impact of New Accounting Stan_2

Impact of New Accounting Standards and Interpretations (Details) - USD ($) $ in Millions	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset	$ 232	$ 205	$ 0
Operating Lease, Liability			$ 210

Accounts Receivable, Net Acco_2

Accounts Receivable, Net Accounts Receivable, Net (Details) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Power receivables		$ 1,401	$ 1,624
Other receivables		128	115
Allowance for uncollectible accounts	[1]	(1)
Accounts receivable, net		1,529	$ 1,739
Available Credit on Public Power Support and Stabilization Program		1,000
Subsequent Credit on Public Power Support and Stabilization Program		$ 1
[1]	Allowance for uncollectible accounts was less than $1 million at September 30, 2020 and 2019, and therefore is not represented in the table above.

Inventories, Net Inventories,_2

Inventories, Net Inventories, Net (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Inventories, Net
Materials and supplies inventory	$ 770	$ 742
Fuel inventory	253	294
RECs inventory, net	15	16
Allowance for inventory obsolescence	(35)	(53)
Inventories, net	$ 1,003	$ 999

Net Completed Plant Net Compl_2

Net Completed Plant Net Completed Plant (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Completed Plant
Completed plant cost	$ 64,970	$ 62,944
Accumulated depreciation	33,550	31,384
Net completed plant	31,420	31,560
Revisions to asset retirement costs	1,100
Coal-fired
Completed Plant
Completed plant cost	18,613	17,400
Accumulated depreciation	13,944	12,538
Net completed plant	4,669	4,862
Gas and oil-fired
Completed Plant
Completed plant cost	6,010	6,054
Accumulated depreciation	1,696	1,562
Net completed plant	4,314	4,492
Nuclear
Completed Plant
Completed plant cost	25,741	25,543
Accumulated depreciation	12,141	11,656
Net completed plant	13,600	13,887
Transmission
Completed Plant
Completed plant cost	8,283	7,932
Accumulated depreciation	3,140	3,083
Net completed plant	5,143	4,849
Hydroelectric
Completed Plant
Completed plant cost	3,410	3,163
Accumulated depreciation	1,090	1,051
Net completed plant	2,320	2,112
Other electrical plant
Completed Plant
Completed plant cost	1,981	1,920
Accumulated depreciation	1,146	1,110
Net completed plant	835	810
Computer Software, Intangible Asset [Member]
Completed Plant
Completed plant cost	3	3
Accumulated depreciation	2	1
Net completed plant	1	2
Multipurpose dams
Completed Plant
Completed plant cost	900	900
Accumulated depreciation	381	373
Net completed plant	519	527
Other stewardship
Completed Plant
Completed plant cost	29	29
Accumulated depreciation	10	10
Net completed plant	$ 19	$ 19

Other Long-Term Assets Other _2

Other Long-Term Assets Other Long-Term Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Other Long-Term Assets
EnergyRight receivables	$ 86	$ 100
Prepaid Expense, Noncurrent	42	22
Restricted Cash and Investments, Noncurrent	21	23
Total other long-term assets	325	325
Impact on secured borrowings	1
Prepaid Expense, Current	3	5
Accounts Receivable [Member]
Other Long-Term Assets
EnergyRight receivables	18	20
Other long-term assets
Other Long-Term Assets
EnergyRight receivables	69	81
Loans and other long-term receivables, net	100	125
Commodity contract derivative assets	23	0
Restricted Cash and Investments, Noncurrent		23
Prepaid capacity payments	11	19
Other	$ 59	$ 55
Energy Right
Other Long-Term Assets
Number of days in default	180 days
Minimum | Energy Right
Other Long-Term Assets
EnergyRight loan terms	5 years
Maximum | Energy Right
Other Long-Term Assets
EnergyRight loan terms	10 years

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Regulatory Assets and Liabilities
Non-current regulatory liabilities	$ 23	$ 0
Accelerated Amortization of Deferred Nuclear Generating Units and Training Costs			$ 857
Accelerated recovery for Kingston ash spill	266
Current regulatory assets	130	156
Regulatory assets	10,245	8,763
Regulatory Assets	10,375	8,919
Current regulatory liabilities	141	150
Regulatory asset amount expensed	23	261	$ 2
Gallatin CCR		672
Regulatory Liabilities	164	150
Reclass Environmental agreements to Other reg assets		12
Deferred Project Costs [Member]
Regulatory Assets and Liabilities
Gallatin coal combustion residual facilities estimated cost to cap and close	114	89
Regulatory Asset
Regulatory Assets and Liabilities
Regulatory assets	138	142
Removal Costs [Member]
Regulatory Assets and Liabilities
Regulatory assets	1,506	1,241
Unrealized losses on interest rate derivatives
Regulatory Assets and Liabilities
Current regulatory assets	4	39
Regulatory assets	0	15
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	2,512	1,741
Pension Costs [Member]
Regulatory Assets and Liabilities
Regulatory assets	5,193	4,756
Deferred Fuel Costs [Member]
Regulatory Assets and Liabilities
Current regulatory assets	12	28
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	896	868
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Non-current regulatory liabilities	23	0
Current regulatory liabilities	26	12
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	$ 115	$ 138

Asset Acquisitions and Busine_2

Asset Acquisitions and Business Combinations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 20, 2017
Business Combinations and Settlement of Preexisting Relationships [Abstract]
Percentage equity interests acquired			100.00%
Total cash consideration	$ 36
Fair value of assets acquired			$ 110
Fair value of liabilities assumed		$ 78	74
Amortization expense of SPE's acquired	1
Loss on extinguishment	$ 3
Lease/leaseback obligations settled			71
Reacquisition price			$ 74

Variable Interest Entities (Det

Variable Interest Entities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2013	Sep. 30, 2012	Jan. 17, 2012
Liabilities
Current maturities of long-term debt of variable interest entities issued at par	$ 41	$ 39
Liabilities, Current	4,711	4,312
Other long-term liabilities	2,548	2,308
Long-term debt of variable interest entities, net	1,048	1,089
VIE Financing
Face Amount	$ 40					$ 100
Rate of Return SHLLC	7.00%
Accrued interest	$ 10	11
Accounts Payable and Accrued Liabilities		1
Liabilities	39,893	38,842
SCCG
VIE Financing
Face Amount				$ 360
Debt and Lease Obligation				$ 400
Holdco
VIE Financing
Face Amount					$ 100
JSCCG
VIE Financing
Face Amount					900
Variable Interest Entity, Primary Beneficiary [Member]
Liabilities
Liabilities, Current	54	53
Other long-term liabilities	23	25
VIE Financing
Accounts Payable and Accrued Liabilities	3	3
Liabilities	1,125	1,167			$ 1,000
Interest Expense	$ (54)	$ (56)	$ (58)

Other Long-Term Liabilities O_2

Other Long-Term Liabilities Other Long-Term Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Other Long-Term Liabilities
Interest rate swaps	$ 2,041	$ 1,764
Derivative Liability	277
Accounts Payable and Accrued Liabilities		1
Capital lease obligations	25	223
Currency swap liabilities	209	208	[1]
EnergyRight financing obligation	108	126
Non-current regulatory liabilities	23	0
Total other long-term liabilities	2,548	2,308
Deferral of EnergyRight laons	1
Finance Lease, Liability	525	182
Other long-term liabilities
Other Long-Term Liabilities
Interest rate swaps	1,927	1,676
Capital lease obligations	171	0
Currency swap liabilities	123	193
EnergyRight financing obligation	78	90
Environmental agreements liability	0	80
Membership interests of VIE subject to mandatory redemption	56	66
Other	193	203
Accounts payable and accrued liabilities
Other Long-Term Liabilities
Interest rate swaps	114	88
Service agreements	15	12
EnergyRight financing obligation	$ 19	$ 23
[1]	See Note 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities .

Asset Retirement Obligations _3

Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Liabilities Settled [Line Items]
Increase in ARO liability		$ 1,200
Change in estimate	[1]	1,077	$ 50
Costs for asbestos			114
Allen West ARO increase		273	33
Paradise ARO increase (decrease)			57
Allen East ARO increase (decrease)			44
Gallatin CCR ARO increase (decrease)		173	672
Additional obligations	[1]		18
Gallatin CCR			672
Balance	[1]	6,785	5,616	$ 4,779
Asset Retirement Obligation, Liabilities Settled	[1]	114	89
Accretion (recorded as regulatory asset)	[1]	206	186
Asset Retirement Obligation, Current		345	163
Amortization and Depreciation of Decontaminating and Decommissioning Assets		169	144	144
Total ARO change due to CCR		129
Change in ARO from operating CCR facilities		38
Change in ARO from inactive CCR facilities		91
Increase in CCR post-closure care		460
Change in plant decommissioning obligations		19
Accounts payable and accrued liabilities
Liabilities Settled [Line Items]
Asset Retirement Obligation, Current		345	163
Nuclear
Liabilities Settled [Line Items]
Revision of estimate (other non nuclear)		0	(250)
Change in estimate			0
Additional obligations			18
Gallatin CCR			0
Balance		3,278	3,136	2,989
Asset Retirement Obligation, Liabilities Settled		1	7
Accretion (recorded as regulatory asset)		143	136
Non-nuclear
Liabilities Settled [Line Items]
Change in estimate		1,077	50
Additional obligations			0
Gallatin CCR			672
Balance		3,507	2,480	$ 1,790
Asset Retirement Obligation, Liabilities Settled		113	82
Accretion (recorded as regulatory asset)		$ 63	$ 50
[1]	(1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Debt and Other Obligations De_2

Debt and Other Obligations Debt and Other Obligations - General (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jan. 17, 2012
Debt Instrument
Interest rate		7.10%
Debt ceiling	$ 30,000
Face Amount	$ 40	$ 100

Debt and Other Obligations De_3

Debt and Other Obligations Debt and Other Obligations - Secured Debt of VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Aug. 09, 2013	Jan. 17, 2012
Portion at Other than Fair Value Measurement [Member]
Variable Interest Entities
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	$ 26	$ 28
Long-term debt of variable interest entities (including current maturities)	1,089	1,128
Face Amount	40			$ 100
Interest rate				7.10%
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	35	37	$ 40
Long-term debt of variable interest entities (including current maturities)	$ 1,419	$ 1,371

Debt and Other Obligations De_4

Debt and Other Obligations Debt and Other Obligations - Secured Notes of SPEs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 20, 2017	Jan. 17, 2012	Nov. 14, 2001	Sep. 27, 2000
Secured notes
Secured notes	$ 40			$ 100
Interest rate				7.10%
Fair value of liabilities assumed	78		$ 74
Notes Payable	0	$ 23
Special purpose entity
Secured notes
Secured notes					$ 272	$ 255
Interest rate					5.572%	7.299%
9/20/17 Business Combination
Secured notes
Notes Payable	$ 23

Debt and Other Obligations De_5

Debt and Other Obligations Debt and Other Obligations - Short-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2019	Sep. 30, 2018
Short-Term Debt, Gross [Line Items]
Short-term debt, net of discounts	$ 57	$ 0	$ 0	$ 0	$ 0	$ 0	$ 922	$ 1,217
Short-term Borrowings Gross	$ 57
Weighted average interest rate - discount notes	0.06%						2.15%	2.05%
Foreign Currency Transaction Gain (Loss), Unrealized	$ 153
Foreign Currency Transaction Gain, before Tax	$ 73

Debt and Other Obligations De_6

Debt and Other Obligations Debt and Other Obligations - Put and Call Options (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)Units
Debt Instrument
Amount of redeemable bond issues outstanding		$ 357
Call price		10000.00%
Bond issues with survivor's option | Units		217,000,000
PARRS 1998 Series D Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 256
PARRS interest rate prior to rate reset	6.75%
PARRS interest rate after rate reset	2.134%
Amount of bonds redeemed	$ 318
PARRS 1999 Series A Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 208
PARRS interest rate prior to rate reset	6.50%
PARRS interest rate after rate reset	2.216%
Amount of bonds redeemed	$ 316

Debt and Other Obligations De_7

Debt and Other Obligations Debt and Other Obligations - Debt Securities Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2020	Jul. 20, 2016	Jan. 17, 2012
Debt Instrument
Issues of power bonds	$ 997	$ 0	$ 998
Face Amount	40										$ 100
Discount on debt issues	(3)	0
Redemptions/Maturities of variable interest entities	39	38	36
Redemptions/Maturities of power bonds	1,427	1,035	1,731
Percent of par value									99.70%
Leaseback obligation settled as a result of acquisition										$ 70
Total Current maturities of power bonds issued at par	1,787	1,030
Interest rate											7.10%
Short-term debt, net of discounts	57	922	$ 1,217	$ 0	$ 0	$ 0	$ 0	$ 0
Current maturities of long-term debt of variable interest entities issued at par	41	39
Current maturities of notes payable	0	23
880591EL2
Debt Instrument
Total Current maturities of power bonds issued at par	$ 1,500	0
Interest rate	3.875%
Debt Instrument, Maturity Date	Feb. 15, 2021
880591DC3
Debt Instrument
Total Current maturities of power bonds issued at par	$ 258	0
Interest rate	5.805%
Debt Instrument, Maturity Date	Jun. 7, 2021
880591EF5 (12.15.20)
Debt Instrument
Total Current maturities of power bonds issued at par	$ 1	0
Debt Instrument, Maturity Date	Dec. 15, 2020
880591EF5
Debt Instrument
Total Current maturities of power bonds issued at par	$ 0	1
Interest rate	3.77%
Debt Instrument, Maturity Date	Dec. 15, 2019
880591EF5 (6.15.21)
Debt Instrument
Debt Instrument, Maturity Date	Jun. 15, 2021
880591EF5 (6/15/2018)
Debt Instrument
Total Current maturities of power bonds issued at par	$ 0	27
Debt Instrument, Maturity Date	Jun. 15, 2020
880591EF5 (6/15/2021)
Debt Instrument
Total Current maturities of power bonds issued at par	$ 28	0
PARRS 1998 Series D Bond
Debt Instrument
Redemptions/Maturities of power bonds	23	0
PARRS 1999 Series A Bond
Debt Instrument
Redemptions/Maturities of power bonds	1,000	0
2020 Series A
Debt Instrument
Redemptions/Maturities of power bonds	$ 1,000	$ 0
Total
Debt Instrument
Debt Instrument, Redemption Period, End Date	1,489	1,119
Percent of par value	100.00%
Debt of variable interest entities
Debt Instrument
Redemptions/Maturities of variable interest entities	$ 39	$ 38
Notes Payable
Debt Instrument
Redemptions/Maturities of notes payable	23	46
electronotes
Debt Instrument
Redemptions/Maturities of power bonds	219	5
2013 Series A [Member]
Debt Instrument
Redemptions/Maturities of power bonds		1,000
2009 Series B
Debt Instrument
Redemptions/Maturities of power bonds	28	30
1997 Series E [Member]
Debt Instrument
Redemptions/Maturities of power bonds	17
1995 Series B
Debt Instrument
Redemptions/Maturities of power bonds	140	0
Total
Debt Instrument
Debt Securities Issues	$ 997	$ 0

Debt and Other Obligations De_8

Debt and Other Obligations Debt and Other Obligations - Debt Outstanding (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2018	Jan. 17, 2012
Short-term debt
Coupon rate										7.10%
Short-term debt, net of discounts		$ 922	$ 57	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,217
Current maturities of long-term debt of variable interest entities issued at par		39	41
Current maturities of notes payable		23	0
Total Current maturities of power bonds issued at par		1,030	1,787
Current maturities of power bonds		1,030	1,787
Total current debt outstanding, net		2,014	1,885
Long-term debt
Long-term power bonds, net		19,094	17,956
Long-term power bonds	[1]	19,225	18,078
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		(131)	(122)
Long-term debt of variable interest entities, net		1,089	1,048
Total long-term debt, net		20,183	19,004
Foreign Currency Transaction Gain (Loss), before Tax		191	$ 80
880591DX7
Short-term debt
Coupon rate	[2]		4.65%
Debt Instrument, Maturity Date			Jun. 15, 2035
Long-term debt
Long-term power bonds, net		436	$ 436
880591EF5
Short-term debt
Coupon rate			3.77%
Debt Instrument, Maturity Date			Jun. 15, 2034
Long-term debt
Long-term power bonds, net		246	$ 218
880591DC3
Short-term debt
Coupon rate			5.805%
Debt Instrument, Maturity Date			Jun. 7, 2021
Long-term debt
Long-term power bonds, net		246	$ 0
880591EL2
Short-term debt
Coupon rate			3.875%
Debt Instrument, Maturity Date			Feb. 15, 2021
Long-term debt
Long-term power bonds, net		1,500	$ 0
electronotes
Long-term debt
Maturity date - earliest			May 15, 2020
Maturity date - latest			Feb. 15, 2043
Call date - earliest			Feb. 15, 2015
Call date - latest			Feb. 15, 2018
Long-term power bonds, net		217	$ 0
880591EN8
Short-term debt
Coupon rate			1.875%
Debt Instrument, Maturity Date			Aug. 15, 2022
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591ER9
Short-term debt
Coupon rate			2.875%
Debt Instrument, Maturity Date			Sep. 15, 2024
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591CJ9
Short-term debt
Coupon rate			6.75%
Debt Instrument, Maturity Date			Nov. 1, 2025
Long-term debt
Long-term power bonds, net		1,350	$ 1,350
880591EU2 [Member]
Short-term debt
Coupon rate			2.875%
Debt Instrument, Maturity Date			Feb. 1, 2027
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591300
Short-term debt
Coupon rate			2.134%
Debt Instrument, Maturity Date			Jun. 1, 2028
Long-term debt
Long-term power bonds, net		273	$ 256
880591409
Short-term debt
Coupon rate			2.216%
Debt Instrument, Maturity Date			May 1, 2029
Long-term debt
Long-term power bonds, net		232	$ 208
880591DM1
Short-term debt
Coupon rate			7.125%
Debt Instrument, Maturity Date			May 1, 2030
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591DV1
Short-term debt
Coupon rate			4.70%
Debt Instrument, Maturity Date			Jul. 15, 2033
Long-term debt
Long-term power bonds, net		472	$ 472
880591DP4
Short-term debt
Coupon rate			6.587%
Debt Instrument, Maturity Date			Jun. 7, 2032
Long-term debt
Long-term power bonds, net		307	$ 323
880591CK6
Short-term debt
Coupon rate			5.98%
Debt Instrument, Maturity Date			Apr. 1, 2036
Long-term debt
Long-term power bonds, net		121	$ 121
880591CS9
Short-term debt
Coupon rate			5.88%
Debt Instrument, Maturity Date			Apr. 1, 2036
Long-term debt
Long-term power bonds, net		1,500	$ 1,500
880591CP5
Short-term debt
Coupon rate			6.15%
Debt Instrument, Maturity Date			Jan. 15, 2038
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591ED0
Short-term debt
Coupon rate			5.50%
Debt Instrument, Maturity Date			Jun. 15, 2038
Long-term debt
Long-term power bonds, net		500	$ 500
880591EH1
Short-term debt
Coupon rate			5.25%
Debt Instrument, Maturity Date			Sep. 15, 2039
Long-term debt
Long-term power bonds, net		2,000	$ 2,000
880591EP3
Short-term debt
Coupon rate			3.50%
Debt Instrument, Maturity Date			Dec. 15, 2042
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591DU3
Short-term debt
Coupon rate			4.962%
Debt Instrument, Maturity Date			Jun. 7, 2043
Long-term debt
Long-term power bonds, net		185	$ 194
880591CF7
Short-term debt
Coupon rate			6.235%
Debt Instrument, Maturity Date			Jul. 15, 2045
Long-term debt
Long-term power bonds, net		140	$ 0
880591EB4
Short-term debt
Coupon rate			4.875%
Debt Instrument, Maturity Date			Jan. 15, 2048
Long-term debt
Long-term power bonds, net		500	$ 500
880591DZ2
Short-term debt
Coupon rate	[2]		5.375%
Debt Instrument, Maturity Date			Apr. 1, 2056
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591EJ7
Short-term debt
Coupon rate			4.625%
Debt Instrument, Maturity Date			Sep. 15, 2060
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591ES7
Short-term debt
Coupon rate			4.25%
Debt Instrument, Maturity Date			Sep. 15, 2065
Long-term debt
Long-term power bonds, net		1,000	$ 1,000
880591EW8 [Member]
Short-term debt
Coupon rate			0.75%
Debt Instrument, Maturity Date			May 15, 2025
Long-term debt
Long-term power bonds, net		0	$ 1,000
880591EF5 (6/15/2018)
Short-term debt
Total Current maturities of power bonds issued at par		27	$ 0
Debt Instrument, Maturity Date			Jun. 15, 2020
880591EF5
Short-term debt
Coupon rate			3.77%
Total Current maturities of power bonds issued at par		1	$ 0
Debt Instrument, Maturity Date			Dec. 15, 2019
88059TEL1
Short-term debt
Coupon rate			2.65%
Total Current maturities of power bonds issued at par		1	$ 0
Debt Instrument, Maturity Date			Nov. 15, 2019
88059TEL1 (5/15/2018)
Short-term debt
Total Current maturities of power bonds issued at par		1	$ 0
Debt Instrument, Maturity Date			May 15, 2020
880591EV0 [Member]
Short-term debt
Coupon rate			2.25%
Total Current maturities of power bonds issued at par		$ 1,000	$ 0
Debt Instrument, Maturity Date			Mar. 15, 2020
Minimum | electronotes
Short-term debt
Coupon rate			2.375%
Maximum | electronotes
Short-term debt
Coupon rate			3.625%
[1]	Includes net exchange gain from currency transactions of $80 million and $191 million at September 30, 2020 and 2019
[2]	The coupon rate represents TVA's effective interest rate.

Debt and Other Obligations De_9

Debt and Other Obligations Debt and Other Obligations - Maturities Due (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2018
Debt Instrument
2018		$ 1,901
2019		1,071
2020		69
2021		1,058
2022		1,059
Thereafter		15,957
Total		21,115
Short-term debt, net of discounts	$ 922	57	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,217
Short-term debt, net of discounts total		57
Foreign Currency Transaction Gain (Loss), before Tax	$ 191	80
Net discount on sale of Bonds		77
Foreign Currency Transaction Gain (Loss), Unrealized		153
Power bonds
Debt Instrument
Debt issuance costs		45
Other long-term debt
Debt Instrument
Debt issuance costs		$ 8

Debt and Other Obligations D_10

Debt and Other Obligations Debt and Other Obligations - Credit Facility Agreements (Details)	Sep. 30, 2020USD ($)Credit_facilities	Sep. 30, 2019USD ($)
Credit Facility Agreements
Current borrowing capacity	$ 150,000,000
Line of Credit
Credit Facility Agreements
Current borrowing capacity	150,000,000
Revolving Credit Facilities
Credit Facility Agreements
Current borrowing capacity	2,650,000,000
Credit facility agreements borrowings outstanding	$ 0
Number of revolving credit facilities | Credit_facilities	4
Revolving Credit Facility 4	$ 150,000,000
Revolving credit facility 3	1,000,000,000
Revolving credit facility 1	500,000,000
Revolving Credit Facility 2	1,000,000,000
Long-term Line of Credit, Borrowings 4	0
Long-term Line of Credit, Borrowings 3	0
Long-term Line of Credit, Borrowings 1	0
Long-term Line of Credit, Borrowings 2	0
Line of Credit Facility, Remaining Borrowing Capacity 4	112,000,000
Line of Credit Facility, Remaining Borrowing Capacity 2	568,000,000
Line of Credit Facility, Remaining Borrowing Capacity 3	513,000,000
Line of Credit Facility, Remaining Borrowing Capacity 1	0
Line of Credit Facility, Remaining Borrowing Capacity	1,193,000,000
Letter of Credit
Credit Facility Agreements
Amount of letters of credit outstanding	1,457,000,000	$ 1,300,000,000
Letters of Credit Outstanding, Amount 4	38,000,000
Letters of Credit Outstanding, Amount 3	487,000,000
Letters of Credit Outstanding, Amount 1	500,000,000
Letter of Credit Outstanding, Amount 2	$ 432,000,000

Debt and Other Obligations D_11

Debt and Other Obligations Debt and Other Obligations - Lease/Leasebacks (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 20, 2017	Jul. 20, 2016
Lease/Leasebacks [Abstract]
Percentage equity interests acquired			100.00%
Leaseback obligation settled as a result of acquisition				$ 70
CT and QTE outstanding leaseback obligation	$ 223	$ 263

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Reclassification on cash flow hedges from AOCI to interest expense	$ 38	$ 45	$ 26

Risk Management Activities an_3

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Receive Hedge Accounting Treatment (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Summary of Derivative Instruments That Receive Hedge Accounting Treatment
Interest rate swaps	$ 2,041,000,000	$ 1,764,000,000
Net unrealized gain (loss) on future cash flow hedges	(1,000,000)	(114,000,000)	$ 10,000,000
Reclassification to earnings from cash flow hedges	38,000,000	45,000,000	$ 26,000,000
Ineffective portion excluded from testing	0
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	27,000,000
Accounts payable and accrued liabilities
Summary of Derivative Instruments That Receive Hedge Accounting Treatment
Interest rate swaps	$ 114,000,000	$ 88,000,000

Risk Management Activities an_4

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details)	12 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2020USD ($)
Derivative
Unrealized gains/losses on derivatives	$ 0
Change in Unrealized gains (losses) on Interest Rate Derivatives	272,000,000	$ (565,000,000)
Interest rate swaps	2,041,000,000	1,764,000,000
Interest Rate Swap
Derivative
Amount of gain (loss) recognized in income on derivatives	(97,000,000)	(79,000,000)
Fair value	(588,000,000)	(498,000,000)
Commodity Contract Derivatives
Derivative
Amount of gain (loss) recognized in income on derivatives	(1,000,000)	0
Fair value	$ 46,000,000	$ (41,000,000)
Coal Contract Derivatives
Derivative
Number of contracts	0	8
Notional amount	0	9,000,000
Fair value	$ 0	$ (4,000,000)	$ 10,000,000
Natural Gas Contract Derivatives
Derivative
Number of contracts	42	65
Notional amount	302,000,000	330,000,000
Fair value	$ 46,000,000	$ (37,000,000)
Accounts payable and accrued liabilities
Derivative
Interest rate swaps	114,000,000	88,000,000
Accounts payable and accrued liabilities | Interest Rate Swap
Derivative
Fair value	(32,000,000)	(24,000,000)
Accounts payable and accrued liabilities | Commodity Contract Derivatives
Derivative
Fair value	$ (3,000,000)	$ (37,000,000)

Risk Management Activities an_5

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Mark-to-Market Values of TVA Derivatives (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	$ 2,250
Other Credit Derivatives [Member] | Other long-term liabilities
Derivatives, Fair Value
Fair value	49	$ 12
Other Credit Derivatives [Member] | Other current assets
Derivatives, Fair Value
Fair value	1,927	1,676
200 million Sterling currency swap
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	209
Fair value	(78)	(90)
200 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	0	(84)
200 million Sterling currency swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(78)	(6)
250 million Sterling currency swap
Derivatives, Fair Value
Fair value	(63)	(61)
250 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(58)	(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	(68)	(57)
150 million Sterling currency swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(65)	(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	(1,449)	(1,261)
$1.0 billion notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(1,369)	(1,199)
$1.0 billion notional interest rate swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(80)	(62)
$476 million notional interest rate swap
Derivatives, Fair Value
Fair value	(588)	(498)
$476 million notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(556)	(474)
$476 million notional interest rate swap | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(32)	(24)
$42 million notional interest rate swap
Derivatives, Fair Value
Fair value	(4)	(5)
$42 million notional interest rate swap | Other long-term liabilities
Derivatives, Fair Value
Fair value	(2)	(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	46	(41)
Commodity contract derivatives | Other long-term assets
Derivatives, Fair Value
Fair value	26	0
Commodity contract derivatives | Other long-term liabilities
Derivatives, Fair Value
Fair value	0	(16)
Commodity contract derivatives | Other current assets
Derivatives, Fair Value
Fair value	23	12
Commodity contract derivatives | Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	$ (3)	$ (37)

Risk Management Activities an_6

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Currency Swaps Outstanding (Details) £ in Millions	12 Months Ended
	Sep. 30, 2020GBP (£)Bond_issues
Derivative
Number of British pound sterling denominated bond transactions | Bond_issues	3
1999 Currency Swap Contract
Derivative
Effective Date of Currency Swap Contract	1999
Associated TVA bond issues currency exposure	£ 200
Expiration Date of Swap	2021
Overall effective cost to TVA	5.81%
2001 Currency Swap Contract
Derivative
Effective Date of Currency Swap Contract	2001
Associated TVA bond issues currency exposure	£ 250
Expiration Date of Swap	2032
Overall effective cost to TVA	6.59%
2003 Currency Swap Contract
Derivative
Effective Date of Currency Swap Contract	2003
Associated TVA bond issues currency exposure	£ 150
Expiration Date of Swap	2043
Overall effective cost to TVA	4.96%

Risk Management Activities an_7

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Counterparty Credit Risk (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)megawattsCustomers	Sep. 30, 2019USD ($)
Derivative
Receivables from power sales | $	$ 1,401	$ 1,624
Credit of Customers
Derivative
Number of customers that represent the percent of sales | Customers	2
Percent of total sales by customers	17.00%
Long-term Contract for Purchase of Electric Power [Domain]
Derivative
Megawatts | megawatts	440

Risk Management Activities an_8

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Letter of Credit
Offsetting Assets [Line Items]
Amount of letters of credit outstanding	$ 1,457	$ 1,300
Other Contract
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets, subject to master netting or similar arrangements	$ 49
Net Amounts of Assets Presented in the Balance Sheet		$ 12

Risk Management Activities an_9

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities, subject to master netting or similar arrangements		$ 2,250
Derivative Liability			$ 2,025
Total derivatives not subject to master netting or similar arrangement		3	53
Total		2,253
Currency Swap
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities, subject to master netting or similar arrangements		209
Derivative Liability	[1]		208
Interest Rate Contract
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities, subject to master netting or similar arrangements		2,041
Derivative Liability	[1]		1,764
Total derivatives subject to master netting or similar arrangement
Offsetting Liabilities [Line Items]
Derivative Liability			1,972
Letter of Credit
Offsetting Liabilities [Line Items]
Amount of letters of credit outstanding		$ 1,457	$ 1,300
[1]	Letters of credit of approximately $1.5 billion and $1.3 billion were posted as collateral at September 30, 2020 and 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.

Risk Management Activities a_10

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Other Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 13	$ 22
Fair Value, Inputs, Level 2
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 13	$ 22

Risk Management Activities a_11

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative
Likely collateral obligation increase if downgraded	$ 22
Collateralized Securities [Member]
Derivative
Aggregate fair value of derivative instruments with credit-risk related contingent features that were in a liability position	2,200
Collateral obligations	1,500
Letter of Credit
Derivative
Amount of letters of credit outstanding	$ 1,457	$ 1,300

Fair Value Measurements - Inves

Fair Value Measurements - Investments (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Long-term Investments	$ 3,198	$ 2,968
Balance in the NDT	2,200
Balance in the ART	$ 866
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
Fair value of gross plan assets	$ 8,368	8,472
Number of readily available quoted exchange prices for the investments	0
Increase in NDT	$ 123
LTDCP
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Unrealized gains (losses) on investments	2	(2)
SERP
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Unrealized gains (losses) on investments	3	0
ART
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Unrealized gains (losses) on investments	32	(70)
NDT
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Unrealized gains (losses) on investments	37	$ (112)
Equity Funds [Member]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Commitments, Fair Value Disclosure	218
Real Estate Funds [Member]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Commitments, Fair Value Disclosure	67
Credit [Member]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Commitments, Fair Value Disclosure	33
Private equity
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Commitments, Fair Value Disclosure	133
Private real estate funds
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value of gross plan assets	54
Private Credit [Member]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Commitments, Fair Value Disclosure	16
Interest Payments relating to energy prepayment obligations
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
2019	$ 4

Fair Value Measurements - Nonpe

Fair Value Measurements - Nonperformance Risk (Details) $ in Millions	Sep. 30, 2020USD ($)
Nonperformance Risk
Derivative credit valuation adjustment, assets	$ 1
Derivative credit valuation adjustment, liabilities	$ 1

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Investments
Equity securities	$ 500	$ 464
Government debt securities	525	344
Corporate debt securities	356	417
Mortgage and asset-backed securities	27	32
Institutional mutual funds	188	250
Forward debt securities contracts - asset	13	22
Private equity funds measured at net asset value	194	140
Private real estate measured at net asset value	168	135
Private credit measured at net asset value	53	33
Commingled funds measured at net asset value	1,174	1,131
Total investments	3,198	2,968
Commodity contract derivatives	49	12
Total	3,247	2,980
Liabilities
Currency swaps	209	208	[1]
Interest rate swaps	2,041	1,764
Commodity contract derivatives	3	53
Total	2,253	2,025
Fair Value, Inputs, Level 1
Investments
Equity securities	500	464
Government debt securities	485	279
Corporate debt securities	0	0
Mortgage and asset-backed securities	0	0
Institutional mutual funds	188	250
Forward debt securities contracts - asset	0	0
Private equity funds measured at net asset value	0	0	[2]
Private real estate measured at net asset value	0	0	[2]
Private credit measured at net asset value	0	0
Commingled funds measured at net asset value	0	0	[2]
Total investments	1,173	993
Commodity contract derivatives	0	0
Total	1,173	993
Liabilities
Currency swaps	0	0	[1]
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	40	65
Corporate debt securities	356	417
Mortgage and asset-backed securities	27	32
Institutional mutual funds	0	0
Forward debt securities contracts - asset	13	22
Private equity funds measured at net asset value	0	0	[2]
Private real estate measured at net asset value	0	0	[2]
Private credit measured at net asset value	0	0
Commingled funds measured at net asset value	0	0	[2]
Total investments	436	536
Commodity contract derivatives	49	7
Total	485	543
Liabilities
Currency swaps	209	208	[1]
Interest rate swaps	2,041	1,764
Commodity contract derivatives	3	44
Total	2,253	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 - asset	0	0
Private equity funds measured at net asset value	0	0	[2]
Private real estate measured at net asset value	0	0	[2]
Private credit measured at net asset value	0	0
Commingled funds measured at net asset value	0	0	[2]
Total investments	0	0
Commodity contract derivatives	0	5
Total	0	5
Liabilities
Currency swaps	0	0	[1]
Interest rate swaps	0	0
Commodity contract derivatives	0	9
Total	$ 0	$ 9
[1]	See Note 15 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities .
[2]	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.

Fair Value Measurements - Fai_2

Fair Value Measurements - Fair Value Measurements Using Significant Unobservable Inputs (Details) tons-per-year in Billions	12 Months Ended
	Sep. 30, 2020USD ($)tons-per-year	Sep. 30, 2019USD ($)tons-per-year	Sep. 30, 2018USD ($)
Fair Value Measurements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	$ (1,000,000)
Commodity contract derivatives, assets	49,000,000	$ 12,000,000
Commodity contract derivatives, liabilities	$ 3,000,000	$ 53,000,000
Minimum
Assets
Fair value measurements tons per year | tons-per-year	0.4	0.7
Price per ton	$ 12.10	$ 12.25
Liabilities
Fair value measurements tons per year | tons-per-year	0.4	0.7
Price per ton	$ 12.10	$ 12.25
Maximum
Assets
Fair value measurements tons per year | tons-per-year	0.8	0.8
Price per ton	$ 94.51	$ 112.24
Liabilities
Fair value measurements tons per year | tons-per-year	0.8	0.8
Price per ton	$ 94.51	$ 112.24
Commodity Contract Derivatives
Fair Value Measurements
Balance at beginning/end of period	0	(4,000,000)	$ 58,000,000
Change in net unrealized gains (losses) deferred as regulatory assets and liabilities	5,000,000	(62,000,000)
Fair Value, Inputs, Level 3
Fair Value Measurements
Commodity contract derivatives, assets	0	5,000,000
Commodity contract derivatives, liabilities	$ 0	$ 9,000,000

Fair Value Measurements - Estim

Fair Value Measurements - Estimated Values of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Aug. 09, 2013
Estimated Values of Financial Instruments (Level 2 Valuation)
EnergyRight receivables (including current portion)	$ 86	$ 100
Financing Receivable, after Allowance for Credit Loss	93	120
EnergyRight® financing obligations (including current portion)	108	126
Unfunded Loan Commitments	2	10
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	35	37	$ 40
Long-term outstanding power bonds (including current maturities), net	26,630	26,059
Long-term debt of variable interest entities (including current maturities)	1,419	1,371
Long-term notes payable (including current maturities)	0	23
Portion at Other than Fair Value Measurement [Member]
Estimated Values of Financial Instruments (Level 2 Valuation)
EnergyRight receivables (including current portion)	87	101
Financing Receivable, after Allowance for Credit Loss	105	131
EnergyRight® financing obligations (including current portion)	97	113
Unfunded Loan Commitments	0	0
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	26	28
Long-term outstanding power bonds (including current maturities), net	19,743	20,124
Long-term debt of variable interest entities (including current maturities)	1,089	1,128
Long-term notes payable (including current maturities)	$ 0	$ 23

Proprietary Capital (Details)

Proprietary Capital (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Appropriation Investment
Amount of appropriation investment that was repaid	$ 1,000								$ 1,000
Remaining appropriation investment	258								258
Balance at beginning of year				$ 11,625				$ 10,283	11,625	$ 10,283	$ 9,133
Net income (loss)	700	$ 205	$ 255	192	$ 588	$ 165	$ 241	423	1,352	1,417	1,119
Return on power program appropriation investment									(6)	(6)	(5)
Balance at end of year	12,932				11,625				12,932	11,625	$ 10,283
Net proprietary capital at September 30	$ 12,932				$ 11,625				$ 12,932	$ 11,625
Computed average interest rate payable	2.44%				2.37%				2.44%	2.37%	2.09%
Nonpower Programs Appropriation Investment
Appropriation Investment
Balance at beginning of year				4,351					$ 4,351
Balance at end of year	$ 4,351				$ 4,351				4,351	$ 4,351
Power Program Appropriation Investment
Appropriation Investment
Balance at beginning of year				258				258	258	258	$ 258
Net income (loss)									0	0	0
Return on power program appropriation investment									0	0	0
Balance at end of year	258				258				258	258	258
Power Program Retained Earnings
Appropriation Investment
Balance at beginning of year				10,823				9,404	10,823	9,404	8,282
Net income (loss)									1,360	1,425	1,127
Return on power program appropriation investment									(6)	(6)	(5)
Balance at end of year	12,177				10,823				12,177	10,823	9,404
Net proprietary capital at September 30	12,435				11,081				12,435	11,081
Nonpower Programs Appropriation Investment, Net
Appropriation Investment
Balance at beginning of year				556				564	556	564	572
Net income (loss)									(8)	(8)	(8)
Return on power program appropriation investment									0	0	0
Balance at end of year	548				556				548	556	564
Nonpower Programs Retained Earnings
Appropriation Investment
Balance at beginning of year				$ (3,795)				$ (3,787)	(3,795)	(3,787)
Return on power program appropriation investment									0	0
Balance at end of year	(3,803)				(3,795)				(3,803)	(3,795)	(3,787)
Net proprietary capital at September 30	$ 548				$ 556				548	556
Affiliated Entity
Appropriation Investment
Return on power program appropriation investment									$ (6)	$ (6)	$ (5)

Proprietary Capital - Accumulat

Proprietary Capital - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss)
Net effect on earnings	$ 0	$ 0
Net unrealized gain (loss) on future cash flow hedges		(1)	$ (114)	$ 10
Reclassification to earnings from cash flow hedges		38	$ 45	$ 26
Reclassification to earnings from cash flow hedges in the next twelve months		$ (27)

Other Income (Expense), Net O_2

Other Income (Expense), Net Other Income (Expense), Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other Income (Expense), Net
Change in other income (expense)	$ (26)
Other income		$ 21	$ 0
Proceeds from Other Deposits	0	21
Interest income	18	25	23
External services	12	13	14
Gain (Loss) on Investments	9	3	6
Miscellaneous		0	7
Miscellaneous	(3)
Total other income (expense), net	36	$ 62	$ 50
Change in interest income	$ 7

Benefit Plans Components of Ben

Benefit Plans Components of Benefit Plans (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Fixed and variable fund annual maximum contribution		$ 10,000
Defined contribution plan contribution amount	$ 92,000,000	$ 88,000,000	$ 84,000,000	$ 80,000,000
Minimum
Defined Benefit Plan Disclosure
Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach		10.00%

Benefit Plans Obligations and F

Benefit Plans Obligations and Funded Status (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Amount related to change in number of participants		$ 7
Pension Benefits
Change in benefit obligation
Benefit obligation		13,675	$ 13,312
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation		13,312	11,725
Service cost		55	44	$ 53
Interest cost		415	499	$ 473
Plan participants' contributions		6	7
Change in Plan Assets due to Collections	[1]	0	0
Collections	[1]	0	0
Actuarial loss (gain)		614	1,756
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		2	7
Net transfers from variable fund/401(k) plan		2	1
Expenses paid		(5)	(6)
Benefits paid		726	721
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets		7,959	7,980
Change in plan assets
Fair value of net plan assets		7,980	7,980
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets			8,003
Actual return on plan assets		397	389
Employer contributions		305	307
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		$ (5,716)	$ (5,332)
Discount rate		2.75%	3.20%	4.35%
Amount of defined benefit plan actuarial gain (loss) from change in COLA		$ 69
Amount of defined benefit plan actuarial gain (loss) from discount rate change		(714)	$ (1,600)
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption		(137)	(14)
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience		74	147
Amount of defined benefit plan actuarial gain (loss) from assumption change in elections		32
Other Post-retirement Benefits
Change in benefit obligation
Benefit obligation		544	499
Postconfirmation, Other Postretirement Obligations		499	428
Service cost		16	11	$ 14
Interest cost		16	18	$ 19
Plan participants' contributions		0	0
Change in Plan Assets due to Collections	[1]	20	22
Collections	[1]	20	22
Actuarial loss (gain)		39	78
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0	0
Net transfers from variable fund/401(k) plan		0	0
Expenses paid		0	0
Benefits paid		46	58
Change in plan assets
Fair value of net plan assets		0	0
Actual return on plan assets		0	0
Employer contributions		26	36
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		$ (544)	$ (499)
Discount rate		3.05%	3.30%
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions		$ (30)	$ (24)
Amount of change related to actual		4	7
Amount of defined benefit plan actuarial gain (loss) from discount rate change		$ (20)	$ (71)
Defined Benefit Plan, Assumptions Used in Calculation, Description		3.05	3.30 percent	4.40
Amount of defined benefit plan actuarial gain (loss) from change in health care trend rate assumptions		$ 15	$ 24
[1]	Collections include retiree contributions as well as provider discounts and rebates.

Benefit Plans Amounts Recognize

Benefit Plans Amounts Recognized on TVA's Consolidated Balance Sheets (Details) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure
Regulatory assets		$ 10,245	$ 8,763
Non-current regulatory liabilities		(23)	0
Accounts payable and accrued liabilities		(1,844)	(1,649)
Pension and post-retirement benefit obligations		(6,617)	(6,181)
Pension Benefits
Defined Benefit Plan Disclosure
Amount capitalized due to actions of regulator		110	95
Regulatory assets		5,115	4,731
Accounts payable and accrued liabilities		(5)	(5)
Pension and post-retirement benefit obligations	[1]	(5,711)	(5,327)
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Amount capitalized due to actions of regulator		0	0
Regulatory assets			25
Non-current regulatory liabilities		(78)
Accounts payable and accrued liabilities		(28)	(28)
Pension and post-retirement benefit obligations	[1]	(516)	(471)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent
Defined Benefit Plan Disclosure
Postemployment benefits liability, noncurrent		$ 390	$ 383
[1]	The table above excludes $390 million and $383 million of post-employment benefit costs that are recorded in Post-retirement and post-employment benefit obligations on the Consolidated Balance Sheets at September 30, 2020 and 2019, respectively.

Benefit Plans Postretirement Be

Benefit Plans Postretirement Benefit Costs Deferred as Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure
Regulatory assets	$ (10,245)	$ (8,763)
Non-current regulatory liabilities	23	0
Pension Benefits
Defined Benefit Plan Disclosure
Unrecognized prior service cost (credit)	(615)	(714)
Unrecognized net loss	5,620	5,350
Amount capitalized due to actions of regulator	(110)	(95)
Regulatory assets	(5,115)	(4,731)
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Unrecognized prior service cost (credit)	(112)	(135)
Unrecognized net loss	190	160
Amount capitalized due to actions of regulator	0	0
Regulatory assets		$ (25)
Non-current regulatory liabilities	$ 78

Benefit Plans Projected Benefit

Benefit Plans Projected Benefit Obligations and Accumulated Benefit Obligations in Exess of Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure
Projected benefit obligation		$ 13,312
Accumulated benefit obligation	$ 13,613	13,246
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	7,959	7,980
Fair value of net plan assets	$ 7,980	$ 7,980

Benefit Plans Components of Net

Benefit Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 55	$ 44	$ 53
Interest cost	415	499	473
Expected return on plan assets	488	477	478
Amortization of prior service credit	(97)	(99)	(99)
Recognized net actuarial loss	(436)	(336)	(409)
Net periodic benefit cost as acutarially determined	321	303	358
Amount expensed (capitalized) due to actions of regulator	15	(1)	54
Total net period benefit cost	306	304	304
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Service cost	16	11	14
Interest cost	16	18	19
Expected return on plan assets	0	0	0
Amortization of prior service credit	(24)	(24)	(22)
Recognized net actuarial loss	(10)	4	8
Net periodic benefit cost as acutarially determined	18	9	19
Amount expensed (capitalized) due to actions of regulator	0	0	0
Total net period benefit cost	$ 18	$ 9	$ 19

Benefit Plans Expected Amortiza

Benefit Plans Expected Amortization of Regulatory Assets in Next Fiscal Year (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Defined Benefit Plan Disclosure
Prior service cost (credit)	$ (115)
Net actuarial loss	459
Defined Benefit Plan Amortization From Regulatory Assets Of Amounts Capitalized due to Actions of Regulatory	28
Pension Benefits
Defined Benefit Plan Disclosure
Prior service cost (credit)	(97)
Net actuarial loss	447
Defined Benefit Plan Amortization From Regulatory Assets Of Amounts Capitalized due to Actions of Regulatory	28
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Prior service cost (credit)	(18)
Net actuarial loss	12
Defined Benefit Plan Amortization From Regulatory Assets Of Amounts Capitalized due to Actions of Regulatory	$ 0

Benefit Plans Actuarial Assumpt

Benefit Plans Actuarial Assumptions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	25.00%
Pension Benefits
Defined Benefit Plan Disclosure
Discount rate	3.20%	4.35%	3.85%
Discount rate	2.75%	3.20%	4.35%
Rate of compensation increase	3.43%	3.50%
Expected return on plan assets	6.75%	6.75%	6.75%
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.43%	3.50%	5.34%
COLA percentage increase (decrease)	600.00%
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Discount rate	3.30%	4.40%	3.95%
Discount rate	3.05%	3.30%
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Minimum
Defined Benefit Plan Disclosure
Rate of compensation increase	2.50%
Maximum
Defined Benefit Plan Disclosure
Rate of compensation increase	14.00%
Pre-Medicare Eligible [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Current health care cost trend rate(2)	6.75%	6.25%	6.50%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027	2027
Initial health care cost trend rate	$ 0.0650	$ 0.0675
Post-Medicare Eligible [Member] [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Current health care cost trend rate(2)	0.00%	0.00%	0.00%
Ultimate health care cost trend rate	4.00%	4.00%	4.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2024	2023

Benefit Plans Sensitivity to Ce

Benefit Plans Sensitivity to Certain Changes in Pension Assumptions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	25.00%
Discount rate
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 17,000,000
Impact on Projected Benefit Obligation	$ 418,000,000
Rate of return on plan assets
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 18,000,000
Cost of Living Adjustments [Domain]
Defined Benefit Plan Disclosure
Change in Assumption	0.25%
Impact on Pension Cost	$ 30,000,000
Impact on Projected Benefit Obligation	$ 270,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Discount rate	3.05%	3.30%
Actuarial assumption COLA	$ 1.54	$ 0.0221	$ 0.0184
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
COLA percentage increase (decrease)	600.00%
Discount rate	2.75%	3.20%	4.35%
Pre-Medicare Eligible [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%	5.00%

Benefit Plans Sensitivity to Ch

Benefit Plans Sensitivity to Changes in Assumed Health Care Cost Trend Rates (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Maximum
Defined Benefit Plan Disclosure
Effect of one percentage point increase on total service and interest cost components	$ 4
Effect of one percentage point increase on end-of-year accumulated postretirement benefit obligation	70
Minimum
Defined Benefit Plan Disclosure
Effect of one percentage point decrease on total service and interest cost components	(4)
Effect of one percentage point decrease on end-of-year accumulated postretirement benefit obligation	$ (68)

Benefit Plans Asset Holdings (D

Benefit Plans Asset Holdings (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Target Allocation	100.00%
Plan Asset Allocations	100.00%	100.00%
Global public equity
Defined Benefit Plan Disclosure
Target Allocation	32.00%
Plan Asset Allocations	36.00%	37.00%
Public real assets
Defined Benefit Plan Disclosure
Target Allocation	10.00%
Plan Asset Allocations	10.00%	15.00%
Private equity
Defined Benefit Plan Disclosure
Target Allocation	8.00%
Plan Asset Allocations	13.00%	10.00%
Safety oriented fixed income
Defined Benefit Plan Disclosure
Target Allocation	20.00%
Plan Asset Allocations	18.00%	18.00%
Opportunistic fixed income
Defined Benefit Plan Disclosure
Target Allocation	20.00%
Plan Asset Allocations	15.00%	12.00%
Private real assets
Defined Benefit Plan Disclosure
Target Allocation	10.00%
Plan Asset Allocations	8.00%	8.00%
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Actuarial assumption COLA	$ 1.54	$ 0.0221	$ 0.0184

Benefit Plans Fair Value Measur

Benefit Plans Fair Value Measurements (Details) $ in Millions		12 Months Ended
		Sep. 30, 2020USD ($)Years	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Defined Benefit Plan Disclosure
Fair value of gross plan assets		$ 8,368	$ 8,472
Estimated future decommissioning cost	[1]	6,785	5,616	$ 4,779
Derivative liabilities		135	136
Net payables		107	132
Payables for collateral on loaned securities		$ 167	224
Voting percentage required to desolve partnership in private equity		80.00%
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		$ 2,679	2,670
Derivative liabilities		1	4
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2,561	2,800
Derivative liabilities		134	132
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		42	58
Estimated future decommissioning cost		94	42
Derivative liabilities		0	0
Equity securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,624	1,766
Equity securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,621	1,762
Equity securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	4
Preferred securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		11	10
Preferred securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	1
Preferred securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		11	9
Preferred securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Corporate debt securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,421	1,387
Corporate debt securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Corporate debt securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,418	1,382
Corporate debt securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	5
Residential mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		317	427
Residential mortgage-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Residential mortgage-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		314	424
Residential mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	3
Debt securities issued by U.S. Treasury and other U.S. government agencies
Defined Benefit Plan Disclosure
Fair value of gross plan assets		701	807
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		701	807
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Asset-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		116	144
Asset-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Asset-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		88	116
Asset-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		28	28
Debt securities issued by state/local governments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		23	18
Debt securities issued by state/local governments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by state/local governments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		23	18
Debt securities issued by state/local governments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by foreign governments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		231	210
Debt securities issued by foreign governments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by foreign governments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		179	209
Debt securities issued by foreign governments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		52	1
Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		91	81
Commercial mortgage-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commercial mortgage-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		86	80
Commercial mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		5	1
Equity security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		931	795
Equity security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		203	308
Debt security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commodity commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets			217
Commodity commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Commodity commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Commodity commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Blended security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		102	125
Blended security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Blended security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Blended security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Institutional mutual funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		277	97
Institutional mutual funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		277	97
Institutional mutual funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Institutional mutual funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Cash equivalents and other short-term investments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		338	329
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		77	1
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		261	328
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Certificates of deposit
Defined Benefit Plan Disclosure
Fair value of gross plan assets			3
Certificates of deposit | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Certificates of deposit | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			3
Certificates of deposit | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Private Credit [Member]
Defined Benefit Plan Disclosure
Fair value of gross plan assets		166	78
Private Credit [Member] | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private Credit [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private Credit [Member] | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,003	778
Private equity funds measured at net asset value | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		629	659
Private real estate funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Securities lending commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		167	224
Securities lending commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Securities lending commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		167	224
Securities lending commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Futures
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	2
Derivative liabilities		1	4
Futures | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	2
Derivative liabilities		1	4
Futures | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Futures | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Purchased options
Defined Benefit Plan Disclosure
Fair value of gross plan assets		10
Purchased options | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Purchased options | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		10
Purchased options | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Interest Rate Swap
Defined Benefit Plan Disclosure
Derivative liabilities		6	12
Interest Rate Swap | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Interest Rate Swap | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Derivative liabilities		6	12
Interest Rate Swap | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Foreign currency forward
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2	1
Derivative liabilities		3	1
Foreign currency forward | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Foreign currency forward | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2	1
Derivative liabilities		3	1
Foreign currency forward | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Written options
Defined Benefit Plan Disclosure
Fair value of gross plan assets			5
Written options | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Written options | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			5
Written options | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Credit default swaps
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2
Derivative liabilities		2	1
Credit default swaps | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Derivative liabilities		0	0
Credit default swaps | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2
Derivative liabilities		2	1
Credit default swaps | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Derivative liabilities		0	0
Securities Sold under Agreements to Repurchase [Member]
Defined Benefit Plan Disclosure
Derivative liabilities		123	118
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Derivative liabilities		123	118
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Derivative liabilities		$ 0	$ 0
Minimum
Defined Benefit Plan Disclosure
Number of years partnerships in private equity generally continue | Years		10
Number of one year extensions for partnerships in private equity | Years		2
Maximum
Defined Benefit Plan Disclosure
Number of years partnerships in private equity generally continue | Years		14
Number of one year extensions for partnerships in private equity | Years		3
[1]	(1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Benefit Plans Fair Value Meas_2

Benefit Plans Fair Value Measurements Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure
Net payables	$ 107	$ 132
Payables for collateral on loaned securities	167	224
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of gross plan assets	8,368	8,472
Private equity reclassed to private real asset		113
Private real estate reclassed to private real asset		546
Fair Value, Inputs, Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of gross plan assets	42	58
Net realized/unrealized gains	46	4
Purchases, sales, issuances, and settlements, net	11	(12)
Transfers in and/or out of Level 3	(5)	$ (8)
Fair value of net plan assets	$ 94

Benefit Plans Estimated Future

Benefit Plans Estimated Future Benefit Payments (Details) $ in Millions	Sep. 30, 2020USD ($)
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 777
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	776
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	773
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	768
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	767
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	3,741
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	28
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	26
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	24
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	23
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	22
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	$ 117

Benefit Plans Contributions (De

Benefit Plans Contributions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Defined contribution plan contribution amount	$ 92,000,000	$ 88,000,000	$ 84,000,000	$ 80,000,000
Other postretirement benefit contributions		25,000,000	36,000,000
Contribution related to TVARS case		5,000,000	4,000,000
Expected Payment for Postretirement Benefits	28,000,000
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Payments Related to SERP	5,000,000
Defined Benefit Plan, Related to SERP		5,000,000	7,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Employer contributions		26,000,000	36,000,000
Pension Benefits
Defined Benefit Plan Disclosure
Employer contributions		305,000,000	$ 307,000,000
Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		300,000,000
Minimum | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		$ 300,000,000
Scenario, Forecast | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions	$ 300,000,000

Benefit Plans Other Postemploym

Benefit Plans Other Postemployment Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other Post-Employment Benefits
Discount rate		0.69%	1.68%	3.05%
Period expense		$ 45	$ 59	$ 6
Postemployment benefits liability			419	$ 339
Payment of Workers Compensation Claims	$ 32	74	39
Accounts Payable and Accrued Liabilities
Other Post-Employment Benefits
Postemployment Benefits Liability, Current		0	36
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent
Other Post-Employment Benefits
Postemployment benefits liability, noncurrent		$ 390	$ 383

Commitments and Contingencies -

Commitments and Contingencies - Table (Details) $ in Millions		Sep. 30, 2020USD ($)megawatts	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Obligations
Megawatts provided under transmission obligations | megawatts		1,450
Accrual for Environmental Loss Contingencies, Gross		$ 14	$ 15
Estimated future decommissioning cost	[1]	6,785	5,616	$ 4,779
Operating Leases, Future Minimum Payments Due, Next Twelve Months		66	76
Operating Leases, Future Minimum Payments, Due in Two Years		51	75
Operating Leases, Future Minimum Payments, Due in Three Years		39	60
Operating Leases, Future Minimum Payments, Due in Four Years		37	12
Operating Leases, Future Minimum Payments, Due in Five Years		34	3
Operating Leases, Future Minimum Payments, Due Thereafter		16	2
Total		243	228
CT and QTE outstanding leaseback obligation		223	263
Other Commitment, to be Paid, Year One		207
Other Commitment, to be Paid, Year Two		25
Other Commitment, to be Paid, Year Three		0
Other Commitment, to be Paid, Year Four		0
Other Commitment, to be Paid, Year Five		0
Other Commitment, to be Paid, after Year Five		0
Total		232
Nuclear
Obligations
Estimated future decommissioning cost		$ 3,278	$ 3,136	$ 2,989
[1]	(1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Commitments and Contingencies_2

Commitments and Contingencies - Energy Prepayment Obligations (Details) $ in Millions	Sep. 30, 2020USD ($)
Interest Payments relating to energy prepayment obligations
Obligations
2019	$ 4

Commitments and Contingencies_3

Commitments and Contingencies - Membership Interests of VIE Subject to Mandatory Redemption (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Aug. 09, 2013
Portion at Other than Fair Value Measurement [Member]
Long-term Purchase Commitment [Line Items]
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	$ 26	$ 28
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	35	$ 37	$ 40
Minimum payments on membership interests subject to mandatory redemption, due in next twelve months	3
Other Commitment	232
Minimum payments on membership interests subject to mandatory redemption, due in year two	3
Minimum payments on membership interests subject to mandatory redemption, due in year three	2
Minimum payments on membership interests subject to mandatory redemption, due in year four	1
Minimum payments on membership interests subject to mandatory redemption, due in year five	$ 1

Commitments and Contingencies_4

Commitments and Contingencies - Leases (Details) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Leases
Other Commitment, to be Paid, Year One		$ 207
CT and QTE outstanding leaseback obligation		223	$ 263
Operating Leases, Future Minimum Payments Due, Next Twelve Months		66	76
Operating Leases, Future Minimum Payments, Due in Two Years		51	75
Operating Leases, Future Minimum Payments, Due in Three Years		39	60
Operating Leases, Future Minimum Payments, Due in Four Years		37	12
Operating Leases, Future Minimum Payments, Due in Five Years		34	3
Operating Leases, Future Minimum Payments, Due Thereafter		16	2
Total		243	228
Other Commitment, to be Paid, Year Two		25
Other Commitment, to be Paid, Year Three		0
Other Commitment, to be Paid, Year Four		0
Other Commitment, to be Paid, Year Five		0
Other Commitment, to be Paid, after Year Five		0
Other Commitment		232
Estimated future decommissioning cost	[1]	$ 6,785	$ 5,616	$ 4,779
[1]	(1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Commitments and Contingencies_5

Commitments and Contingencies - Purchase Obligations (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)Megawattsmegawatts	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Obligations
Megawatts provided under power purchase obligations	2,384
Remaining terms of the agreements, high end of range	12 years
Megawatts provided under transmission obligations | megawatts	1,450
Power purchased under agreement | $	$ 202	$ 195	$ 188
Purchase Agreements Required by Federal Law
Obligations
Megawatts provided under power purchase obligations	268
Number of generation sources under PPAs	111

Commitments and Contingencies_6

Commitments and Contingencies - Contingencies (Details) $ in Millions		12 Months Ended
		Sep. 30, 2020USD ($)reactorsProceduresInsurance_layersUnits	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Contingencies
Loss Contingency, Damages Sought, Value		$ 30
Nuclear liability insurance		450
Assessment from licensees for each licensed reactor		$ 138
Number of licensed reactors in US | reactors		97
Nuclear accident assessment limitation per year per unit		$ 20
Number of licensed nuclear units | Units		7
Maximum assessment per nuclear incident		$ 963
Total amount of protection available		$ 13,800
Number of layers until the U.S. Congress is required to take action | Insurance_layers		2
Amount of insurance available for loss at any one site		$ 2,100
Maximum amount of retrospective premiums		145
Maximum idemnity if a covered accident tasks or keeps a nuclear unit offline		490
Maximum amount of retrospective premiums		43
Estimated future decommissioning cost	[1]	$ 6,785	$ 5,616	$ 4,779
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures		2
Amount spent to reduce emissions since 1970		$ 6,800
Amount spent to reduce emissions		19	17	62
Possible additional future costs for compliance with Clean Air Act requirements		156
Possible additional future costs for compliance with CCR requirements		949
Possible additional future costs for compliance with Clean Water requirements.		190
Estimated liability for cleanup and similar environmental work on a non-discounted basis		14	15
Amount of insurance available for loss at any one site, max		2,800
Nuclear
Contingencies
Estimated future decommissioning cost		3,278	3,136	2,989
Non-nuclear
Contingencies
Estimated future decommissioning cost		$ 3,507	$ 2,480	$ 1,790
[1]	(1) Includes $345 million a nd $163 million at September 30, 2020 and 2019, respectively, in Current liabilities.

Commitments and Contingencies_7

Commitments and Contingencies - Legal Proceedings (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)AgreementsGroups	Sep. 30, 2019USD ($)
Legal Proceedings
Possible additional future costs for compliance with CCR requirements	$ 949
Amount spent under environmental agreements	280
Contribution related to TVARS case	5	$ 4
Possible additional future costs for compliance with Clean Water requirements.	190
Amount remaining to be spent under environmental agreements	11
Loss Contingency, Damages Sought, Value	30
General
Legal Proceedings
Legal loss contingency accrual	$ 14
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
Amount to be invested in certain environmental projects	$ 290
Other long-term liabilities | General
Legal Proceedings
Legal loss contingency accrual	12
Accounts payable and accrued liabilities | General
Legal Proceedings
Legal loss contingency accrual	$ 2

Commitments and Contingencies U

Commitments and Contingencies Unfunded loan commitments (Details) $ in Millions	Sep. 30, 2020USD ($)
Legal Proceedings
2018	$ 1
Energy prepayment obligations
Legal Proceedings
Prepayment Obligations	$ 10

Related Parties Related Parti_2

Related Parties Related Parties (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Related Parties
Remaining appropriation investment	$ 258								$ 258
Current borrowing capacity	150								150
Revenue from sales of electricity	2,899	$ 2,251	$ 2,521	$ 2,578	$ 3,239	$ 2,604	$ 2,750	$ 2,725	10,249	$ 11,318	$ 11,233
Other income										21	0
Long-term Investments	3,198				2,968				3,198	2,968
Return on power program appropriation investment									(6)	(6)	(5)
Related Party Transactions
Related Parties
Revenue from sales of electricity									105	118	122
Other income									260	258	240
Operating expenses									224	222	220
Additions to property, plant, and equipment									9	10	8
Cash and cash equivalents	31				45				31	45	46
Receivables from Customers	94				76				94	76	60
Long-term Investments	485				279				485	279	199
Receivables, Long-term Contracts or Programs	27				53				27	53	46
Accounts payable and accrued liabilities	39				69				39	69	69
Long-term power bonds, net	$ 1				$ 0				1	0	0
Return on power program appropriation investment									$ (6)	$ (6)	$ (5)

Unaudited Quarterly Financial_3

Unaudited Quarterly Financial Information Unaudited Quarterly Financial Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue from sales of electricity	$ 2,899	$ 2,251	$ 2,521	$ 2,578	$ 3,239	$ 2,604	$ 2,750	$ 2,725	$ 10,249	$ 11,318	$ 11,233
Operating expenses	1,862	1,716	1,914	2,046	2,301	2,088	2,158	1,960	7,538	8,507	8,665
Operating income	1,037	535	607	532	938	516	592	765	2,711	2,811	2,568
Net income (loss)	$ 700	$ 205	$ 255	$ 192	$ 588	$ 165	$ 241	$ 423	$ 1,352	$ 1,417	$ 1,119

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other revenue										$ 145	$ 159	$ 158
Off-system sales										4	4	7
Sales of Electricity (subtotal)										10,100	11,155	11,079
Electric revenue										(10,104)	(11,159)	(11,075)
Revenue Capitalized During Pre-Commercial Operations										0	0	11
Revenues	$ 2,899	$ 2,251	$ 2,521	$ 2,578	$ 3,239	$ 2,604	$ 2,750	$ 2,725		10,249	11,318	11,233
Pandemic Relief Credit									$ 200
ALABAMA
Electric revenue										(1,439)	(1,593)	(1,600)
GEORGIA
Electric revenue										(249)	(270)	(267)
KENTUCKY
Electric revenue										(624)	(691)	(696)
MISSISSIPPI
Electric revenue										(941)	(1,063)	(1,052)
NORTH CAROLINA
Electric revenue										(65)	(74)	(66)
TENNESSEE
Electric revenue										(6,740)	(7,419)	(7,350)
VIRGINIA
Electric revenue										$ (42)	$ (45)	$ (48)

Revenue Customer Type (Details)

Revenue Customer Type (Details) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020USD ($)Units	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2020USD ($)Units	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2004USD ($)
Electric revenue									$ 10,104	$ 11,159	$ 11,075
Other revenue									145	159	158
Revenues	$ 2,899	$ 2,251	$ 2,521	$ 2,578	$ 3,239	$ 2,604	$ 2,750	$ 2,725	$ 10,249	11,318	11,233
Percent of sales of electricity to LPCs									93.00%
Bill credits for LTA									$ (163)	(14)	0
Number of LPCs signed LTA | Units	142								142
Percentage of total operating revenues									91.80%
Total number of LPCs | Units	153								153
Number of LPCs signed Flexibility Agreement | Units	64								64
Revenue Capitalized During Pre-Commercial Operations									$ 0	$ 0	(11)
MLGW's % of operating revenues									9.00%
NES's % of operating revenues									8.00%
MLGW prepayment												$ 1,500
20-year contract arrangement [Member]
Percentage of total operating revenues									74.80%
5-year contract arrangement [Member]
Number of LPCs signed LTA | Units	11								11
Percentage of total operating revenues									17.00%
MLGW
Deferred Revenue, Description									10 million	100 million		100 million
TENNESSEE
Electric revenue									$ 6,740	$ 7,419	7,350
VIRGINIA
Electric revenue									42	45	48
NORTH CAROLINA
Electric revenue									65	74	66
MISSISSIPPI
Electric revenue									941	1,063	1,052
KENTUCKY
Electric revenue									624	691	696
GEORGIA
Electric revenue									249	270	267
ALABAMA
Electric revenue									1,439	1,593	1,600
Federal agencies and other [Member]
Electric revenue									110	122	129
20-year contract arrangement [Member]
Electric revenue									7,666
5-year contract arrangement [Member]
Electric revenue									1,740
Local Power Company [Member]
Electric revenue									9,406	10,351	10,262
Industries Directly Served [Member]
Electric revenue									588	686	695
Capitalized revenue during pre-commercial plant operations [Member]
Electric revenue									$ 0	$ 0	$ 11

Revenue Local Power Company Con

Revenue Local Power Company Contracts (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)Units	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Number of LPCs signed LTA | Units	142
Electric revenue	$ 10,104	$ 11,159	$ 11,075
Total number of LPCs | Units	153
Percentage of total operating revenues	91.80%
20-year contract arrangement [Member]
Electric revenue	$ 7,666
5-year contract arrangement [Member]
Electric revenue	1,740
Local Power Company [Member]
Electric revenue	$ 9,406	$ 10,351	$ 10,262
5-year contract arrangement [Member]
Number of LPCs signed LTA | Units	11
Percentage of total operating revenues	17.00%

Revenue Energy Prepayment Oblig

Revenue Energy Prepayment Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2004
Energy Prepayment Obligation [Line Items]
Electric revenue	$ 10,104	$ 11,159	$ 11,075
Energy Prepayment Discount	$ 4	$ 46
MLGW
Energy Prepayment Obligation [Line Items]
Deferred Revenue, Description	10 million	100 million		100 million

Revenue Economic Development In

Revenue Economic Development Incentives (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenues	$ 318	$ 310
Unpaid economic incentives	$ 172	$ 157

Plant Closures (Details)

Plant Closures (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Abstract]
Accelerated depreciation	$ 387	$ 566
Completed Plant
Accelerated depreciation	$ 387	$ 566
Property, Plant and Equipment [Member]
Completed Plant
Property, Plant and Equipment, Dispositions	11 million	151 million
Property, Plant and Equipment, Disposals	$ 2	$ 19

Leases (Details)

Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Oct. 01, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset	$ 232	$ 0		$ 205
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	516
Total lease assets	748
Accounts Payable and Accrued Liabilities		1
Operating Lease, Liability, Noncurrent	171
Finance Lease, Liability, Noncurrent	525
Total lease liabilities	800
Operating Lease, Cost	84
Variable Lease, Cost	75
Short-term Lease, Cost	7
Finance Lease, Right-of-Use Asset, Amortization	15
Finance Lease, Interest Expense	33
Total finance lease costs	48
Lease, Cost	214
Operating Leases, Rent Expense		97	$ 92
Operating Lease, Liability		$ 210
Operating lease liability
Lessee, Lease, Description [Line Items]
Accounts Payable and Accrued Liabilities	63
Finance lease liability
Lessee, Lease, Description [Line Items]
Accounts Payable and Accrued Liabilities	$ 41

Leases, SoCF (Details)

Leases, SoCF (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Lessee, Lease, Description [Line Items]
Operating cash flows for operating leases	$ 85
Operating cash flows for finance leases	33
Financing cash flows for finance leases	15
Lease assets obtained in exchange for lease obligations - finance	394
Lease assets obtained in exchange for lease obligations - operating	$ 110

Leases, Weighted Averages (Deta

Leases, Weighted Averages (Details)	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	5 years
Finance Lease, Weighted Average Remaining Lease Term	12 years
Operating Lease, Weighted Average Discount Rate, Percent	1.60%
Finance Lease, Weighted Average Discount Rate, Percent	21.80%

Leases, Future Minimum Payments

Leases, Future Minimum Payments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 66	$ 76
Operating Leases, Future Minimum Payments, Due in Two Years	51	75
Operating Leases, Future Minimum Payments, Due in Three Years	39	60
Operating Leases, Future Minimum Payments, Due in Four Years	37	12
Operating Leases, Future Minimum Payments, Due in Five Years	34	3
Operating Leases, Future Minimum Payments, Due Thereafter	16	2
Total	243	228
Present value of future minimum lease payments, operating	(9)	0
Operating present value of net minimum lease payments	234	228
Finance Lease, Liability, to be Paid, Year One	92	53
Finance Lease, Liability, to be Paid, Year Two	93	53
Finance Lease, Liability, to be Paid, Year Three	92	53
Finance Lease, Liability, to be Paid, Year Four	87	55
Finance Lease, Liability, to be Paid, Year Five	86	51
Finance Lease, Liability, Payments Due Thereafter	592	418
Finance Lease, Liability, Payment, Due	1,042	683
Finance Lease, Liability, Payment Amounts Representing Interest	(476)	(495)
Finance present value of net minimum lease payments	566	$ 188
Purchased Power Lease	$ 89

Uncategorized Items - tve-20200

Label	Element	Value
SCCG [Member]
Debt Instrument, Interest Rate, Stated Percentage	us-gaap_DebtInstrumentInterestRateStatedPercentage	3.846%
Holdco [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid	$ 10,000,000
JSCCG [Member]
Debt Instrument, Interest Rate	tve_DebtInstrumentInterestRate	4.626%