Summary of Significant Accounting Policies - (Policies)	6 Months Ended
Nov. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company	The CompanyNational Rural Utilities Cooperative Finance Corporation (“CFC”) is a tax-exempt, member-owned cooperative association incorporated under the laws of the District of Columbia in April 1969. CFC’s principal purpose is to provide its members with financing to supplement the loan programs of the Rural Utilities Service (“RUS”) of the United States Department of Agriculture (“USDA”). CFC makes loans to its rural electric members so they can acquire, construct and operate electric distribution systems, electric generation and transmission (“power supply”) systems and related facilities. CFC also provides its members with credit enhancements in the form of letters of credit and guarantees of debt obligations. As a cooperative, CFC is owned by and exclusively serves its membership, which consists of not-for-profit entities or subsidiaries or affiliates of not-for-profit entities.
Basis of Presentation	Basis of Presentation and Use of Estimates The accompanying unaudited interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and for interim financial statements. These consolidated financial statements include the accounts of CFC, variable interest entities (“VIEs”) where CFC is the primary beneficiary and subsidiary entities created and controlled by CFC to hold foreclosed assets. National Cooperative Services Corporation (“NCSC”) and Rural Telephone Finance Cooperative (“RTFC”) are VIEs that are required to be consolidated by CFC. NCSC is a taxable member-owned cooperative that may provide financing to members of CFC, government or quasi-government entities which own electric utility systems that meet the Rural Electrification Act definition of “rural,” and for-profit and nonprofit entities that are owned, operated or controlled by, or provide significant benefits to certain members of CFC. RTFC is a taxable Subchapter T cooperative association that provides financing for its rural telecommunications members and their affiliates. CFC has not had entities that held foreclosed assets since fiscal year 2017. All intercompany balances and transactions have been eliminated. Unless stated otherwise, references to “we,” “our” or “us” relate to CFC and its consolidated entities.
Use of Estimates	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and related disclosures during the period. Management’s most significant estimates and assumptions involve determining the allowance for credit losses. These estimates are based on information available as of the date of the consolidated financial statements. While management makes its best judgments, actual amounts or results could differ from these estimates. In the opinion of management, these unaudited interim financial statements reflect all adjustments of a normal, recurring nature that are necessary for the fair statement of results for the periods presented.
Reclassification	Certain reclassifications and updates may have been made to the presentation of information in prior periods to conform to the current period presentation.
COVID-19	COVID-19 The COVD-19 pandemic continues to persist. Although most of the initial restrictions imposed at the onset of the pandemic in the U.S. have been relaxed or lifted as a result of the distribution of vaccines, there has been a resurgence of COVID-19 cases fueled by the recently identified, highly transmissible Omicron variant and the continued spread of the Delta variant. Many states throughout the U.S. are currently experiencing record-breaking levels of COVID-19 cases due to the accelerated spread of these variants, which has led some state and local governments to reinstitute measures and restrictions to slow the transmission and mitigate public health risks in certain jurisdictions. We continue to closely monitor developments; however, we cannot predict the future impact of COVID-19 on our operational and financial performance, or the specific ways the pandemic may uniquely impact our members, all of which continue to involve significant uncertainties that depend on future developments, which include, among others, the severity and duration of the current COVID-19 resurgence and its impact on the overall economy and other industry sectors; vaccination rates; the longer-term efficacy of vaccinations; and the potential emergence of new, more transmissible or severe variants.
New Accounting Standards	New Accounting Standards Amendments of Certain Securities and Exchange (“SEC”) Disclosure Guidance In August 2021, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2021-06, Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services—Investment Companies (Topic 946), Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures About Acquired and Disposed Businesses, and No.33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants. This update amends certain SEC disclosure guidance that is included in the accounting standards codification to reflect the SEC’s recent issuance of rules intended to modernize and streamline disclosure requirements. We adopted the SEC’s guidance on the presentation of financial statements and update of statistical disclosures for bank and savings and loan registrants in conjunction with the completion of our Annual Report on Form 10-K for the fiscal year ended May 31, 2021 (“2021 Form 10-K”), which we filed with the SEC on July 30, 2021. The adoption of this disclosure guidance did not have a material impact on our consolidated financial statements. Reference Rate Reform On March 12, 2020, the Financial Accounting Standards Board issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional expedients and exceptions for applying U.S. GAAP on contracts, hedging relationships and other transactions subject to modification due to the expected discontinuance of the London Interbank Offered Rate (“LIBOR”) and other reference rate reform changes to ease the potential accounting and financial burdens related to the expected transition in market reference rates. This guidance permits entities to elect not to apply certain modification accounting requirements to contracts affected by reference rate transition, if certain criteria are met. An entity that makes this election would not be required to remeasure modified contracts at the modification date or reassess a previous accounting determination. The guidance was effective upon issuance on March 12, 2020, and can generally be applied through December 31, 2022. We expect to apply certain of the practical expedients and are in the process of evaluating the timing and application of those elections. Based on our current assessment, we do not believe that the application of this guidance will have a material impact on our consolidated financial statements.
Accounting for Derivatives	Accounting for Derivatives In accordance with the accounting standards for derivatives and hedging activities, we record derivative instruments at fair value as either a derivative asset or derivative liability on our consolidated balance sheets. We report derivative asset and liability amounts on a gross basis based on individual contracts, which does not take into consideration the effects of master netting agreements or collateral netting. Derivatives in a gain position are reported as derivative assets on our consolidated balance sheets, while derivatives in a loss position are reported as derivative liabilities. Accrued interest related to derivatives is reported on our consolidated balance sheets as a component of either accrued interest receivable or accrued interest payable. If we do not elect hedge accounting treatment, changes in the fair value of derivative instruments, which consist of net accrued periodic derivative cash settlements expense and derivative forward value amounts, are recognized in our consolidated statements of operations under derivative gains (losses). If we elect hedge accounting treatment for derivatives, we formally document, designate and assess the effectiveness of the hedge relationship. Changes in the fair value of derivatives designated as qualifying fair value hedges are recorded in earnings together with offsetting changes in the fair value of the hedged item and any related ineffectiveness. Changes in the fair value of derivatives designated as qualifying cash flow hedges are recorded as a component of other comprehensive income (“OCI”), to the extent that the hedge relationships are effective, and reclassified from accumulated other comprehensive income (“AOCI”) to earnings using the effective interest method over the term of the forecasted transaction. Any ineffectiveness in the hedging relationship is recognized as a component of derivative gains (losses) in our consolidated statement of operations. We generally do not designate interest rate swaps, which represent the substantial majority of our derivatives, for hedge accounting. Accordingly, changes in the fair value of interest rate swaps are reported in our consolidated statements of operations under derivative gains (losses). Net periodic cash settlements expense related to interest rate swaps are classified as an operating activity in our consolidated statements of cash flows. We typically designate Treasury rate locks as cash flow hedges of forecasted debt issuances or repricings. Changes in the fair value of treasury locks designated as cash flow hedges are recorded as a component of OCI and reclassified from AOCI into interest expense when the forecasted transaction occurs using the effective interest method. Any ineffectiveness is recognized as a component of derivative gains (losses) in our consolidated statements of operations.
Fair Value Measurement	Fair value, also referred to as an exit price, is defined as the price that would be received for an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. The fair value accounting guidance provides a three-level fair value hierarchy for classifying financial instruments. This hierarchy is based on the markets in which the assets or liabilities trade and whether the inputs to the valuation techniques used to measure fair value are observable or unobservable. The fair value measurement of a financial asset or liability is assigned a level based on the lowest level of any input that is significant to the fair value measurement in its entirety. The levels, in priority order based on the extent to which observable inputs are available to measure fair value, are Level 1, Level 2 and Level 3. The accounting guidance for fair value measurements requires that we maximize the use of observable inputs and minimize the use of unobservable inputs in determining fair value.
Transfer Between Levels	Transfers Between Levels We monitor the availability of observable market data to assess the appropriate classification of financial instruments within the fair value hierarchy and transfer between Level 1, Level 2, and Level 3 accordingly. Observable market data includes but is not limited to quoted prices and market transactions. Changes in economic conditions or market liquidity generally will drive changes in availability of observable market data. Changes in availability of observable market data, which also may result in changes in the valuation technique used, are generally the cause of transfers between levels. We did not have any transfers into or out of Level 3 of the fair value hierarchy during the six months ended November 30, 2021 and 2020.

Summary of Significant Accounting Policies - (Policies)

6 Months Ended

Nov. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The CompanyNational Rural Utilities Cooperative Finance Corporation (“CFC”) is a tax-exempt, member-owned cooperative association incorporated under the laws of the District of Columbia in April 1969. CFC’s principal purpose is to provide its members with financing to supplement the loan programs of the Rural Utilities Service (“RUS”) of the United States Department of Agriculture (“USDA”). CFC makes loans to its rural electric members so they can acquire, construct and operate electric distribution systems, electric generation and transmission (“power supply”) systems and related facilities. CFC also provides its members with credit enhancements in the form of letters of credit and guarantees of debt obligations. As a cooperative, CFC is owned by and exclusively serves its membership, which consists of not-for-profit entities or subsidiaries or affiliates of not-for-profit entities.

Basis of Presentation

Basis of Presentation and Use of Estimates

The accompanying unaudited interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and for interim financial statements. These consolidated financial statements include the accounts of CFC, variable interest entities (“VIEs”) where CFC is the primary beneficiary and subsidiary entities created and controlled by CFC to hold foreclosed assets. National Cooperative Services Corporation (“NCSC”) and Rural Telephone Finance Cooperative (“RTFC”) are VIEs that are required to be consolidated by CFC. NCSC is a taxable member-owned cooperative that may provide financing to members of CFC, government or quasi-government entities which own electric utility systems that meet the Rural Electrification Act definition of “rural,” and for-profit and nonprofit entities that are owned, operated or controlled by, or provide significant benefits to certain members of CFC. RTFC is a taxable Subchapter T cooperative association that provides financing for its rural telecommunications members and their affiliates. CFC has not had entities that held foreclosed assets since fiscal year 2017. All intercompany balances and transactions have been eliminated. Unless stated otherwise, references to “we,” “our” or “us” relate to CFC and its consolidated entities.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and related disclosures during the period. Management’s most significant estimates and assumptions involve determining the allowance for credit losses. These estimates are based on information available as of the date of the consolidated financial statements. While management makes its best judgments, actual amounts or results could differ from these estimates. In the opinion of management, these unaudited interim financial statements reflect all adjustments of a normal, recurring nature that are necessary for the fair statement of results for the periods presented.

Reclassification

Certain reclassifications and updates may have been made to the presentation of information in prior periods to conform to the current period presentation.

COVID-19

The COVD-19 pandemic continues to persist. Although most of the initial restrictions imposed at the onset of the pandemic in the U.S. have been relaxed or lifted as a result of the distribution of vaccines, there has been a resurgence of COVID-19 cases fueled by the recently identified, highly transmissible Omicron variant and the continued spread of the Delta variant. Many states throughout the U.S. are currently experiencing record-breaking levels of COVID-19 cases due to the accelerated spread of these variants, which has led some state and local governments to reinstitute measures and restrictions to slow the transmission and mitigate public health risks in certain jurisdictions. We continue to closely monitor

developments; however, we cannot predict the future impact of COVID-19 on our operational and financial performance, or the specific ways the pandemic may uniquely impact our members, all of which continue to involve significant uncertainties that depend on future developments, which include, among others, the severity and duration of the current COVID-19 resurgence and its impact on the overall economy and other industry sectors; vaccination rates; the longer-term efficacy of vaccinations; and the potential emergence of new, more transmissible or severe variants.

New Accounting Standards

Amendments of Certain Securities and Exchange (“SEC”) Disclosure Guidance

In August 2021, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2021-06, Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services—Investment Companies (Topic 946), Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures About Acquired and Disposed Businesses, and No.33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants. This update amends certain SEC disclosure guidance that is included in the accounting standards codification to reflect the SEC’s recent issuance of rules intended to modernize and streamline disclosure requirements. We adopted the SEC’s guidance on the presentation of financial statements and update of statistical disclosures for bank and savings and loan registrants in conjunction with the completion of our Annual Report on Form 10-K for the fiscal year ended May 31, 2021 (“2021 Form 10-K”), which we filed with the SEC on July 30, 2021. The adoption of this disclosure guidance did not have a material impact on our consolidated financial statements.

Reference Rate Reform

On March 12, 2020, the Financial Accounting Standards Board issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional expedients and exceptions for applying U.S. GAAP on contracts, hedging relationships and other transactions subject to modification due to the expected discontinuance of the London Interbank Offered Rate (“LIBOR”) and other reference rate reform changes to ease the potential accounting and financial burdens related to the expected transition in market reference rates. This guidance permits entities to elect not to apply certain modification accounting requirements to contracts affected by reference rate transition, if certain criteria are met. An entity that makes this election would not be required to remeasure modified contracts at the modification date or reassess a previous accounting determination. The guidance was effective upon issuance on March 12, 2020, and can generally be applied through December 31, 2022. We expect to apply certain of the practical expedients and are in the process of evaluating the timing and application of those elections. Based on our current assessment, we do not believe that the application of this guidance will have a material impact on our consolidated financial statements.

Accounting for Derivatives

In accordance with the accounting standards for derivatives and hedging activities, we record derivative instruments at fair value as either a derivative asset or derivative liability on our consolidated balance sheets. We report derivative asset and liability amounts on a gross basis based on individual contracts, which does not take into consideration the effects of master netting agreements or collateral netting. Derivatives in a gain position are reported as derivative assets on our consolidated balance sheets, while derivatives in a loss position are reported as derivative liabilities. Accrued interest related to derivatives is reported on our consolidated balance sheets as a component of either accrued interest receivable or accrued interest payable.

If we do not elect hedge accounting treatment, changes in the fair value of derivative instruments, which consist of net accrued periodic derivative cash settlements expense and derivative forward value amounts, are recognized in our consolidated statements of operations under derivative gains (losses). If we elect hedge accounting treatment for derivatives, we formally document, designate and assess the effectiveness of the hedge relationship. Changes in the fair value of derivatives designated as qualifying fair value hedges are recorded in earnings together with offsetting changes in the fair value of the hedged item and any related ineffectiveness. Changes in the fair value of derivatives designated as qualifying cash flow hedges are recorded as a component of other comprehensive income (“OCI”), to the extent that the hedge relationships are effective, and reclassified from accumulated other comprehensive income (“AOCI”) to earnings using the

effective interest method over the term of the forecasted transaction. Any ineffectiveness in the hedging relationship is recognized as a component of derivative gains (losses) in our consolidated statement of operations.

We generally do not designate interest rate swaps, which represent the substantial majority of our derivatives, for hedge accounting. Accordingly, changes in the fair value of interest rate swaps are reported in our consolidated statements of operations under derivative gains (losses). Net periodic cash settlements expense related to interest rate swaps are classified as an operating activity in our consolidated statements of cash flows.

We typically designate Treasury rate locks as cash flow hedges of forecasted debt issuances or repricings. Changes in the fair value of treasury locks designated as cash flow hedges are recorded as a component of OCI and reclassified from AOCI into interest expense when the forecasted transaction occurs using the effective interest method. Any ineffectiveness is recognized as a component of derivative gains (losses) in our consolidated statements of operations.

Fair Value Measurement

Fair value, also referred to as an exit price, is defined as the price that would be received for an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. The fair value accounting guidance provides a three-level fair value hierarchy for classifying financial instruments. This hierarchy is based on the markets in which the assets or liabilities trade and whether the inputs to the valuation techniques used to measure fair value are observable or unobservable. The fair value measurement of a financial asset or liability is assigned a level based on the lowest level of any input that is significant to the fair value measurement in its entirety. The levels, in priority order based on the extent to which observable inputs are available to measure fair value, are Level 1, Level 2 and Level 3. The accounting guidance for fair value measurements requires that we maximize the use of observable inputs and minimize the use of unobservable inputs in determining fair value.

Transfer Between Levels

Transfers Between Levels

We monitor the availability of observable market data to assess the appropriate classification of financial instruments within the fair value hierarchy and transfer between Level 1, Level 2, and Level 3 accordingly. Observable market data includes but is not limited to quoted prices and market transactions. Changes in economic conditions or market liquidity generally will drive changes in availability of observable market data. Changes in availability of observable market data, which also may result in changes in the valuation technique used, are generally the cause of transfers between levels. We did not have any transfers into or out of Level 3 of the fair value hierarchy during the six months ended November 30, 2021 and 2020.