Fair Value Measurement - Schedule of carrying and fair values for entity's financial instruments (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Assets:
Cash and cash equivalents	$ 248,819	$ 134,712
Cash and cash equivalents	248,819	134,712
Restricted cash	8,599	8,410
Equity securities, at fair value	11,021	11,252
Debt securities trading, at fair value	31,144	113,663
Deferred compensation investments	9,011	8,019
Loans to members, net	38,392,181	37,039,363
Loans to members, net	35,853,501	34,113,178
Accrued interest receivable	264,952	270,222
Accrued interest receivable	264,952	270,222
Derivative assets	554,116	555,855
Total financial assets	39,519,843	38,141,496
Total financial assets	36,981,163	35,215,311
Liabilities:
Short-term borrowings	5,159,771	5,091,416
Short-term borrowings	5,161,495	5,094,451
Long-term debt	28,345,934	27,163,701
Long-term debt	27,715,985	26,415,950
Accrued interest payable	308,506	294,917
Guarantee liability	16,847	14,396
Guarantee liability	18,236	15,321
Derivative liabilities	31,414	51,368
Subordinated deferrable debt	1,310,282	1,329,485
Deferred compensation liability	9,011	8,019
Subordinated deferrable debt	1,317,026	1,341,974
Members’ subordinated certificates	1,128,240	1,184,714
Members’ subordinated certificates	1,128,240	1,184,714
Total financial liabilities	36,310,005	35,138,016
Total financial liabilities	35,689,913	34,406,714
Level 1
Assets:
Cash and cash equivalents	248,819	134,712
Restricted cash	8,599	8,410
Equity securities, at fair value	11,021	11,252
Debt securities trading, at fair value	0	0
Deferred compensation investments	9,011	8,019
Loans to members, net	0	0
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	277,450	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	9,011	8,019
Subordinated deferrable debt	236,320	238,620
Members’ subordinated certificates	0	0
Total financial liabilities	245,331	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	31,144	113,663
Deferred compensation investments	0	0
Loans to members, net	0	0
Accrued interest receivable	264,952	270,222
Derivative assets	554,116	555,855
Total financial assets	850,212	939,740
Liabilities:
Short-term borrowings	5,161,495	5,094,451
Long-term debt	18,993,254	16,737,855
Accrued interest payable	308,506	294,917
Guarantee liability	0	0
Derivative liabilities	31,414	51,368
Deferred compensation liability	0	0
Subordinated deferrable debt	1,080,706	1,103,354
Members’ subordinated certificates	0	0
Total financial liabilities	25,575,375	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	35,853,501	34,113,178
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	35,853,501	34,113,178
Liabilities:
Short-term borrowings	0	0
Long-term debt	8,722,731	9,678,095
Accrued interest payable	0	0
Guarantee liability	18,236	15,321
Derivative liabilities	0	0
Deferred compensation liability	0	0
Subordinated deferrable debt	0	0
Members’ subordinated certificates	1,128,240	1,184,714
Total financial liabilities	$ 9,869,207	$ 10,878,130