Fair Value Measurement - Schedule of Fair Value by Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Feb. 28, 2026	May 31, 2025	Feb. 28, 2025
Assets:
Cash and cash equivalents	$ 240,687	$ 134,712
Cash and cash equivalents	240,687	134,712
Restricted cash	8,547	8,410
Equity securities, at fair value	10,228	11,252
Debt securities trading, at fair value	42,620	113,663
Deferred compensation investments	8,485	8,019
Loans to members, net	38,714,170	37,039,363	$ 36,434,753
Loans to members, net	36,656,864	34,113,178
Accrued interest receivable	260,735	270,222
Accrued interest receivable	260,735	270,222
Derivative assets	418,984	555,855
Total financial assets	39,704,456	38,141,496
Total financial assets	37,647,150	35,215,311
Liabilities:
Short-term borrowings	5,100,828	5,091,416
Short-term borrowings	5,103,943	5,094,451
Long-term debt	28,908,515	27,163,701
Long-term debt	28,736,396	26,415,950
Accrued interest payable	298,444	294,917
Guarantee liability	15,891	14,396
Guarantee liability	17,269	15,321
Derivative liabilities	48,156	51,368
Deferred compensation liability	8,485	8,019
Subordinated deferrable debt	1,209,713	1,329,485
Subordinated deferrable debt	1,229,487	1,341,974
Members’ subordinated certificates	1,127,906	1,184,714
Members’ subordinated certificates	1,127,906	1,184,714
Total financial liabilities	36,717,938	35,138,016
Total financial liabilities	36,570,086	34,406,714
Level 1
Assets:
Cash and cash equivalents	240,687	134,712
Restricted cash	8,547	8,410
Equity securities, at fair value	10,228	11,252
Debt securities trading, at fair value	0	0
Deferred compensation investments	8,485	8,019
Loans to members, net	0	0
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	267,947	162,393
Liabilities:
Short-term borrowings	0	0
Long-term debt	0	0
Accrued interest payable	0	0
Guarantee liability	0	0
Derivative liabilities	0	0
Deferred compensation liability	8,485	8,019
Subordinated deferrable debt	238,050	238,620
Members’ subordinated certificates	0	0
Total financial liabilities	246,535	246,639
Level 2
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Equity securities, at fair value	0	0
Debt securities trading, at fair value	42,620	113,663
Deferred compensation investments	0	0
Loans to members, net	0	0
Accrued interest receivable	260,735	270,222
Derivative assets	418,984	555,855
Total financial assets	722,339	939,740
Liabilities:
Short-term borrowings	5,103,943	5,094,451
Long-term debt	19,378,581	16,737,855
Accrued interest payable	298,444	294,917
Guarantee liability	0	0
Derivative liabilities	48,156	51,368
Deferred compensation liability	0	0
Subordinated deferrable debt	991,437	1,103,354
Members’ subordinated certificates	0	0
Total financial liabilities	25,820,561	23,281,945
Level 3
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Equity securities, at fair value	0	0
Debt securities trading, at fair value	0	0
Deferred compensation investments	0	0
Loans to members, net	36,656,864	34,113,178
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	36,656,864	34,113,178
Liabilities:
Short-term borrowings	0	0
Long-term debt	9,357,815	9,678,095
Accrued interest payable	0	0
Guarantee liability	17,269	15,321
Derivative liabilities	0	0
Deferred compensation liability	0	0
Subordinated deferrable debt	0	0
Members’ subordinated certificates	1,127,906	1,184,714
Total financial liabilities	$ 10,502,990	$ 10,878,130