Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Feb. 28, 2023	May 31, 2022	Feb. 28, 2022
Assets:
Cash and cash equivalents	$ 172,962	$ 153,551
Cash and cash equivalents	172,962	153,551
Restricted cash	7,298	7,563
Equity securities, at fair value	38,002	33,758
Debt securities trading, at fair value	549,124	566,146
Deferred compensation investments	6,377	6,710
Loans to members, net	32,325,532	29,995,826	$ 29,446,995
Loans to members, net	28,703,674	28,595,111
Accrued interest receivable	161,856	111,418
Accrued interest receivable	161,856	111,418
Derivative assets	554,610	222,042
Total financial assets	33,815,761	31,097,014
Total financial assets	30,193,903	29,696,299
Liabilities:
Short-term borrowings	4,899,631	4,981,167
Short-term borrowings	4,900,240	4,978,580
Long-term debt	23,831,978	21,545,440
Long-term debt	22,202,369	21,106,750
Accrued interest payable	233,690	131,950
Guarantee liability	12,628	12,764
Guarantee liability	11,940	13,083
Derivative liabilities	131,075	128,282
Subordinated deferrable debt	986,678	986,518
Subordinated deferrable debt	952,901	960,869
Members’ subordinated certificates	1,223,415	1,234,161
Members’ subordinated certificates	1,223,415	1,234,161
Total financial liabilities	31,319,095	29,020,282
Total financial liabilities	29,655,630	28,553,675
Level 1
Assets:
Cash and cash equivalents	172,962	153,551
Restricted cash	7,298	7,563
Equity securities, at fair value	38,002	33,758
Debt securities trading, at fair value	0	0
Deferred compensation investments	6,377	6,710
Loans to members, net	0	0
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	224,639	201,582
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	235,157	250,800
Members’ subordinated certificates	0	0
Total financial liabilities	235,157	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	549,124	566,146
Deferred compensation investments	0	0
Loans to members, net	0	0
Accrued interest receivable	161,856	111,418
Derivative assets	554,610	222,042
Total financial assets	1,265,590	899,606
Liabilities:
Short-term borrowings	4,400,240	4,978,580
Long-term debt	13,323,038	12,248,695
Accrued interest payable	233,690	131,950
Guarantee liability	0	0
Derivative liabilities	131,075	128,282
Subordinated deferrable debt	717,744	710,069
Members’ subordinated certificates	0	0
Total financial liabilities	18,805,787	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	28,703,674	28,595,111
Accrued interest receivable	0	0
Derivative assets	0	0
Total financial assets	28,703,674	28,595,111
Liabilities:
Short-term borrowings	500,000	0
Long-term debt	8,879,331	8,858,055
Accrued interest payable	0	0
Guarantee liability	11,940	13,083
Derivative liabilities	0	0
Subordinated deferrable debt	0	0
Members’ subordinated certificates	1,223,415	1,234,161
Total financial liabilities	$ 10,614,686	$ 10,105,299