Loans - Schedule of available balances under unadvanced loan commitments (Details) - Unadvanced commitments - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Available Balance	$ 20,013,899	$ 18,219,009
2027	5,697,972
2028	3,427,676
2029	3,768,149
2030	3,259,955
2031	3,763,178
Thereafter	96,969
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Available Balance	11,616,214	10,747,743
2027	4,767,815
2028	2,332,625
2029	1,855,129
2030	1,419,149
2031	1,241,496
Thereafter	0
Long-term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Available Balance	8,397,685	$ 7,471,266
2027	930,157
2028	1,095,051
2029	1,913,020
2030	1,840,806
2031	2,521,682
Thereafter	$ 96,969

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-3

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(c)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.9-06)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
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-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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-Publisher FASB
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