Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2021
Summary of Significant Accounting Policies [Line Items]
Restricted cash	$ 8,301	$ 7,563
Accrued interest receivable	133,000	94,000
Depreciation and amortization	5,000	$ 8,000	$ 8,000
Unamortized capitalized implementation costs	29,000
Capitalized implementation costs, accumulated amortization	1,000
Capitalized implementation costs, amortization	$ 1,000
Minimum
Summary of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Maximum
Summary of Significant Accounting Policies [Line Items]
Estimated useful lives	40 years
RTFC
Summary of Significant Accounting Policies [Line Items]
Effective percentage of tax rate	21.00%	21.00%	21.00%
Deferred tax assets, net (less than $1 million as of May 31, 2022 for RTFC)	$ 8,000	$ 1,000
Deferred tax assets, valuation allowance (less than $1 million as of May 31, 2022)	$ 8,000	$ 1,000
RTFC | Minimum
Summary of Significant Accounting Policies [Line Items]
Percentage of income from patronage sources allocated to borrowers to be retired in cash prior to filing the applicable tax return	20.00%
NCSC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	$ 100
Effective percentage of tax rate	21.00%	21.00%	21.00%
Deferred tax assets, net (less than $1 million as of May 31, 2022 for RTFC)	$ 1,000	$ 1,000
Distribution system members | CFC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	$ 1,000
Service organization members | CFC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	200
Associates | CFC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	1,000
Associates | RTFC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	100
Voting members | RTFC
Summary of Significant Accounting Policies [Line Items]
Membership fees (in dollars per share)	$ 1,000
Unadvanced commitments not subject to material adverse change clauses
Summary of Significant Accounting Policies [Line Items]
Loans and leases receivable unadvanced commitments period, maximum	5 years
Unadvanced commitments
Summary of Significant Accounting Policies [Line Items]
Loans and leases receivable unadvanced commitments period, maximum	5 years