Loans - Credit concentration Narrative (Details) $ in Thousands	12 Months Ended
May 31, 2026 USD ($) borrower loan distribution_system state power_supply_system	May 31, 2025 USD ($) borrower state distribution_system power_supply_system
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 38,422,128	$ 37,079,978
Number of active borrowers \| borrower	903	899
Number of states with active borrowers \| state	49	49
Loans \| Geographic concentration risk \| TEXAS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 6,403,000	$ 6,105,000
Weighted- Average Interest Rate	17.00%	16.00%
Number of active borrowers \| borrower	67	68
Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of active borrowers \| borrower	50	50
Loans receivable commercial and industrial \| Loans \| Customer concentration risk \| 20 largest borrowers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 7,374,000	$ 7,149,000
Weighted- Average Interest Rate	19.00%
Concentration risk number of borrowers \| borrower	20	20
Loans receivable commercial and industrial \| Loans \| Customer concentration risk \| Largest single borrower or controlled group
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted- Average Interest Rate	1.00%	1.00%
Loans receivable commercial and industrial \| Electric \| Loans \| Credit concentration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 37,821,000	$ 36,488,000
Loans receivable commercial and industrial \| Distribution \| Loans \| Customer concentration risk \| 20 largest borrowers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk number of borrowers \| distribution_system	12	14
Loans receivable commercial and industrial \| Power supply \| Loans \| Customer concentration risk \| 20 largest borrowers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk number of borrowers \| power_supply_system	8	6
Loans outstanding \| Loans \| Credit concentration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted- Average Interest Rate	98.00%	98.00%
Loans guaranteed by rural utilities service
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 95,000	$ 105,000
Loans guaranteed by Farmer Mac
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 322,000	346,000
Number of loans that defaulted \| loan	0
Number of defaulted loans put to Farmer Mac for purchase \| loan	0
Loans guaranteed by Farmer Mac \| Loans \| Credit concentration \| 20 largest borrowers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 214,000	$ 155,000
Concentration risk number of borrowers \| borrower	20	20
Loans guaranteed by Farmer Mac \| Loans \| Customer concentration risk \| 20 largest borrowers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 7,160,000	$ 6,994,000
Concentration risk number of borrowers \| borrower	20	20
Loans guaranteed by Farmer Mac \| Loans \| Geographic concentration risk \| TEXAS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 109,000	$ 118,000
Loans Receivable Commercial and Industrial Not Covered By Farmer Mac Standby Repurchase Agreement \| Loans \| Geographic concentration risk \| TEXAS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members	$ 6,294,000	$ 5,987,000

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- Definition

Financing Receivable, before Allowance for Credit Loss, Number of Defaulted Loans Sold

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Financing Receivable, before Allowance for Credit Loss, Number of Defaults

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Number Of States With Active Borrowers

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Number of Active Borrowers

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

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