Variable Interest Entities - Consolidated Assets and Liabilities of VIEs included in CFCs Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands	Nov. 30, 2019	May 31, 2019	Nov. 30, 2018
Variable Interest Entity [Line Items]
Loans to members	$ 26,438,181	$ 25,916,904	$ 25,294,175
Other assets	40,593	53,699
Total assets	27,566,601	27,124,372	$ 26,829,758
Long-term debt	18,434,451	19,210,793
Other liabilities	48,372	50,112
Total liabilities	26,408,707	25,820,490
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Loans to members	1,058,603	1,087,988
Other assets	12,805	10,963
Total assets	1,071,408	1,098,951
Long-term debt	0	6,000
Other liabilities	36,729	33,385
Total liabilities	$ 36,729	$ 39,385