Investment Securities - Narrative (Details) - USD ($)	12 Months Ended
May 31, 2024	May 31, 2023	May 31, 2022	Jul. 18, 2024
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, trading, unrealized gains (losses)	$ 15,000,000	$ (3,000,000)	$ (27,000,000)
Debt securities, trading, realized gain (less than $1 million during FY2023 and FY2022)	0	1,000,000	1,000,000
Debt securities, trading, realized loss	0
Proceeds from sale of debt securities		36,000,000	5,000,000
Equity securities, unrealized gain	$ 1,000,000	$ 2,000,000
Equity securities, unrealized losses			$ 1,000,000
Series C noncumulative preferred stock \| Subsequent event
Debt and Equity Securities, FV-NI [Line Items]
Redemption price per share (in dollars per share)				$ 25.00

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-14

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

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Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-4

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Amount of unrealized loss on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
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-Name Accounting Standards Codification
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The cash inflow associated with the sale of securities classified as trading securities and held for investment purposes. Excludes proceeds from trading securities purchased and held principally for the purpose of selling them in the near term (thus held for only a short period of time).

+ References

No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6B

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