Allowance for Credit Losses - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
Aug. 31, 2023	Aug. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	$ 53,094	$ 67,560
Provision for credit losses	800	3,496
Recoveries	1,032
Allowance for loan loss, ending balance	54,926	71,056
Parent Company
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	49,424	64,825
Provision for credit losses	(102)	3,249
Recoveries	1,032
Allowance for loan loss, ending balance	50,354	68,074
Parent Company \| Distribution
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	14,924	15,781
Provision for credit losses	798	631
Recoveries	0
Allowance for loan loss, ending balance	15,722	16,412
Parent Company \| Power supply
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	33,306	47,793
Provision for credit losses	(904)	2,550
Recoveries	1,032
Allowance for loan loss, ending balance	33,434	50,343
Parent Company \| Statewide and associate
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	1,194	1,251
Provision for credit losses	4	68
Recoveries	0
Allowance for loan loss, ending balance	1,198	1,319
NCSC
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	2,464	1,449
Provision for credit losses	148	116
Recoveries	0
Allowance for loan loss, ending balance	2,612	1,565
RTFC
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan loss, beginning balance	1,206	1,286
Provision for credit losses	754	131
Recoveries	0
Allowance for loan loss, ending balance	$ 1,960	$ 1,417

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

+ Details

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- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 79
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479294/326-20-55-79

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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-Subparagraph (c)(4)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

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- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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