Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Aug. 31, 2023	May 31, 2023	Aug. 31, 2022
Assets:
Cash and cash equivalents	$ 199,552	$ 198,936
Cash and cash equivalents	199,552	198,936
Restricted cash	9,290	8,301
Equity securities, at fair value	36,780	35,494
Debt securities trading, at fair value	425,331	474,875
Deferred compensation investments	7,162	6,660
Loans to members, net	33,041,720	32,478,992	$ 30,616,275
Loans to members, net	29,309,889	29,308,647
Accrued interest receivable	177,351	172,723
Accrued interest receivable	177,351	172,723
Derivative assets	615,866	460,762
Total financial assets	34,513,052	33,836,743
Total financial assets	30,781,221	30,666,398
Liabilities:
Short-term borrowings	5,124,335	4,546,275
Short-term borrowings	5,125,706	4,547,333
Long-term debt	23,874,274	23,946,548
Long-term debt	22,148,726	22,665,551
Accrued interest payable	274,554	212,340
Guarantee liability	13,552	12,973
Guarantee liability	13,088	12,475
Derivative liabilities	108,239	115,074
Subordinated deferrable debt	1,184,197	1,283,436
Subordinated deferrable debt	1,172,990	1,261,141
Members’ subordinated certificates	1,222,026	1,223,126
Members’ subordinated certificates	1,222,026	1,223,126
Total financial liabilities	31,801,177	31,339,772
Total financial liabilities	30,065,329	30,037,040
Level 1
Assets:
Cash and cash equivalents	199,552	198,936
Restricted cash	9,290	8,301
Equity securities, at fair value	36,780	35,494
Debt securities trading, at fair value	0	0
Deferred compensation investments	7,162	6,660
Loans to members, net	0	0
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	252,784	249,391
Liabilities:
Short-term borrowings	0	0
Long-term debt	0	0
Accrued interest payable	0	0
Guarantee liability	0	0
Derivative liabilities	0	0
Subordinated deferrable debt	241,771	240,831
Members’ subordinated certificates	0	0
Total financial liabilities	241,771	240,831
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	425,331	474,875
Deferred compensation investments	0	0
Loans to members, net	0	0
Accrued interest receivable	177,351	172,723
Derivative assets	615,866	460,762
Total financial assets	1,218,548	1,108,360
Liabilities:
Short-term borrowings	4,625,706	4,547,333
Long-term debt	13,395,526	13,527,393
Accrued interest payable	274,554	212,340
Guarantee liability	0	0
Derivative liabilities	108,239	115,074
Subordinated deferrable debt	931,219	1,020,310
Members’ subordinated certificates	0	0
Total financial liabilities	19,335,244	19,422,450
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	29,309,889	29,308,647
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	29,309,889	29,308,647
Liabilities:
Short-term borrowings	500,000	0
Long-term debt	8,753,200	9,138,158
Accrued interest payable	0	0
Guarantee liability	13,088	12,475
Derivative liabilities	0	0
Subordinated deferrable debt	0	0
Members’ subordinated certificates	1,222,026	1,223,126
Total financial liabilities	$ 10,488,314	$ 10,373,759