Investment Securities - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Feb. 28, 2022	Feb. 28, 2021	Feb. 28, 2022	Feb. 28, 2021	May 31, 2021
Debt and Equity Securities, FV-NI [Line Items]
Unrealized loss	$ (9,000)	$ (3,000)	$ (18,000)	$ (2,000)
Proceeds for sale of debt investment securities	3,000	0	5,000	6,000
Realized gains (less than)	1,000		1,000
Realized losses (less than)				1,000
Short-term borrowings	4,428,057		4,428,057		$ 4,582,096
Debt securities trading, at fair value, pledged as collateral	0		0		210,894
Unrealized loss	(2,000)
Unrealized gain		$ 1,000	1,000	$ 2,000
Securities sold under agreements to repurchase
Debt and Equity Securities, FV-NI [Line Items]
Short-term borrowings	$ 0		$ 0		$ 200,115

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
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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 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 on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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 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).

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Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
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