Loans Allowance for Loan Losses Components and Related Loan Investments (Details) - USD ($) $ in Thousands	May 31, 2020	May 31, 2019
Ending balance of the allowance:
Collective allowance	$ 18,292	$ 16,514
Asset-specific allowance	34,833	1,021
Recorded investment in loans:
Collectively evaluated loans	26,512,298	25,893,811
Individually evaluated loans	178,556	11,853
Loans and Leases Receivable, Net of Deferred Income	26,690,854	25,905,664	[1]
Loans and Leases Receivable, Net Amount	26,637,729	25,888,129
Deferred origination costs	11,526	11,240	[1]
CFC
Ending balance of the allowance:
Collective allowance	13,584	13,120
Recorded investment in loans:
Collectively evaluated loans	25,434,193	24,811,415
Individually evaluated loans	173,464	6,261
Loans and Leases Receivable, Net of Deferred Income	25,607,657	24,817,676	[1]
Loans and Leases Receivable, Net Amount	25,560,219	24,804,556
NCSC
Ending balance of the allowance:
Collective allowance	806	2,007
Asset-specific allowance	0	0
Recorded investment in loans:
Collectively evaluated loans	697,862	742,888
Individually evaluated loans	0	0
Loans and Leases Receivable, Net of Deferred Income	697,862	742,888	[1]
Loans and Leases Receivable, Net Amount	697,056	740,881
RTFC
Ending balance of the allowance:
Collective allowance	3,902	1,387
Asset-specific allowance	979	1,021
Recorded investment in loans:
Collectively evaluated loans	380,243	339,508
Individually evaluated loans	5,092	5,592
Loans and Leases Receivable, Net of Deferred Income	385,335	345,100	[1]
Loans and Leases Receivable, Net Amount	$ 380,454	$ 342,692

[1] The interest rate on unadvanced loan commitments is not set until an advance is made; therefore, all long-term unadvanced loan commitments are reported as variable rate. However, the borrower may select either a fixed or a variable rate when an advance on a commitment is made.