Investment Securities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2026	May 31, 2025	May 31, 2024
Investments [Abstract]
Debt securities, trading, unrealized gains (losses)	$ 1	$ 9	$ 15
Proceeds from sale of debt securities	19	14	0
Equity securities, at fair value	11	11
Equity securities, unrealized gain (loss)	$ (1)	$ (1)	$ 1