Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2026	May 31, 2025
Loan Loss Allowance
Allowance for loan loss, rounded amount	$ 30	$ 41
Financing receivable, allowance coverage ratios	0.08%	0.11%
Financing receivable, allowance for credit loss, period increase (decrease)	$ (11)
Credit reserve for unadvanced loan commitments	$ 1	$ 1
Asset-Specific Allowance
Loan Loss Allowance
Financing receivable, allowance coverage ratios	0.95%	28.79%
Financing receivable, allowance for credit loss, period increase (decrease)	$ (9)
Collective Allowance
Loan Loss Allowance
Financing receivable, allowance coverage ratios	0.08%	0.08%
Financing receivable, allowance for credit loss, period increase (decrease)	$ (2)