Loans - Additional Information - Unadvanced Loan Commitments (Details) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2026	May 31, 2026
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unadvanced line of credit commitments as percentage of unadvanced loan commitments	57.00%
Unadvanced line of credit commitments, term	5 years
Unadvanced Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	$ 20,935,075	$ 20,013,899
Commitments to Extend Credit Subject to Material Adverse Change Clause
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	17,027,000	16,288,000
Unadvanced Commitments Not Subject to Material Adverse Change Clauses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	3,908,439	3,726,000
Variable rate \| Unadvanced Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	$ 9,040,261	8,397,685
Financing receivable, loan commitment, term	5 years
Long-term loans \| Unadvanced Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	$ 9,040,261	$ 8,397,685