Fair Value Measurement - Schedule of carrying and fair values for entity's financial instruments (Details) - USD ($) $ in Thousands	May 31, 2023	May 31, 2022
Assets:
Cash and cash equivalents	$ 198,936	$ 153,551
Cash and cash equivalents	198,936	153,551
Restricted cash	8,301	7,563
Equity securities, at fair value	35,494	33,758
Debt securities trading, at fair value	474,875	566,146
Deferred compensation investments	6,660	6,710
Loans to members, net	32,478,992	29,995,826
Loans to members, net	29,308,647	28,595,111
Accrued interest receivable	172,723	111,418
Accrued interest receivable	172,723	111,418
Derivative assets	460,762	222,042
Financial assets	33,836,743	31,097,014
Financial assets	30,666,398	29,696,299
Liabilities [Abstract]
Short-term borrowings	4,546,275	4,981,167
Short-term borrowings	4,547,333	4,978,580
Long-term debt	23,946,548	21,545,440
Long-term debt	22,665,551	21,106,750
Accrued interest payable	212,340	131,950
Guarantee liability	12,973	12,764
Guarantee liability	12,475	13,083
Derivative liabilities	115,074	128,282
Subordinated deferrable debt	1,283,436	986,518
Subordinated deferrable debt	1,261,141	960,869
Members’ subordinated certificates	1,223,126	1,234,161
Members’ subordinated certificates	1,223,126	1,234,161
Financial liabilities	31,339,772	29,020,282
Financial liabilities	30,037,040	28,553,675
Level 1
Assets:
Cash and cash equivalents	198,936	153,551
Restricted cash	8,301	7,563
Equity securities, at fair value	35,494	33,758
Debt securities trading, at fair value	0	0
Deferred compensation investments	6,660	6,710
Loans to members, net	0	0
Accrued interest receivable	0	0
Derivative assets	0	0
Financial assets	249,391	201,582
Liabilities [Abstract]
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	240,831	250,800
Members’ subordinated certificates	0	0
Financial liabilities	240,831	250,800
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	474,875	566,146
Deferred compensation investments	0	0
Loans to members, net	0	0
Accrued interest receivable	172,723	111,418
Derivative assets	460,762	222,042
Financial assets	1,108,360	899,606
Liabilities [Abstract]
Short-term borrowings	4,547,333	4,978,580
Long-term debt	13,527,393	12,248,695
Accrued interest payable	212,340	131,950
Guarantee liability	0	0
Derivative liabilities	115,074	128,282
Subordinated deferrable debt	1,020,310	710,069
Members’ subordinated certificates	0	0
Financial liabilities	19,422,450	18,197,576
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	29,308,647	28,595,111
Accrued interest receivable	0	0
Derivative assets	0	0
Financial assets	29,308,647	28,595,111
Liabilities [Abstract]
Short-term borrowings	0	0
Long-term debt	9,138,158	8,858,055
Accrued interest payable	0	0
Guarantee liability	12,475	13,083
Derivative liabilities	0	0
Subordinated deferrable debt	0	0
Members’ subordinated certificates	1,223,126	1,234,161
Financial liabilities	$ 10,373,759	$ 10,105,299