Loans - Additional Information - Unadvanced Loan Commitments (Details) - USD ($) $ in Thousands	9 Months Ended
	Feb. 28, 2026	May 31, 2025
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	$ 19,213,793	$ 18,219,009
Commitments to Extend Credit Subject to Material Adverse Change Clause
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	15,507,000	14,629,000
Unadvanced Commitments Not Subject to Material Adverse Change Clauses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	3,706,949	3,590,000
Variable rate | Unadvanced Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	$ 8,231,549	7,471,266
Financing receivable, loan commitment, term	5 years
Long-term loans | Unadvanced Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unadvanced commitments	$ 8,231,549	$ 7,471,266