Loans - Schedule of loan portfolio by risk rating category and member class based on available data (Details) - USD ($) $ in Thousands	May 31, 2023	May 31, 2022
Credit Quality
2023	$ 3,305,706
2022	2,884,965
2021	2,279,183
2020	2,249,051
2019	1,553,789
Prior	17,123,317
Revolving Loans	3,123,338
Total loan outstanding	32,519,349	$ 30,051,354
Pass
Credit Quality
2023	3,301,480
2022	2,884,965
2021	2,274,408
2020	2,249,051
2019	1,544,031
Prior	17,009,878
Revolving Loans	2,932,308
Total loan outstanding	32,196,121	29,556,981
Special Mention
Credit Quality
2023	4,226
2022	0
2021	4,775
2020	0
2019	9,758
Prior	24,105
Revolving Loans	168,155
Total loan outstanding	211,019	266,583
Substandard
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	0
Revolving Loans	0
Total loan outstanding	0	0
Doubtful
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	89,334
Revolving Loans	22,875
Total loan outstanding	112,209	227,790
Criticized
Credit Quality
2023	4,226
2022	0
2021	4,775
2020	0
2019	9,758
Prior	113,439
Revolving Loans	191,030
Total loan outstanding	323,228	494,373
CFC
Credit Quality
Total loan outstanding	31,074,687	28,872,875
CFC | Pass
Credit Quality
2023	2,981,308
2022	2,776,275
2021	2,193,673
2020	2,016,627
2019	1,532,465
Prior	16,542,509
Revolving Loans	2,712,194
Total loan outstanding	30,755,051	28,382,594
CFC | Special Mention
Credit Quality
2023	4,226
2022	0
2021	4,775
2020	0
2019	9,758
Prior	20,513
Revolving Loans	168,155
Total loan outstanding	207,427	262,491
CFC | Doubtful
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	89,334
Revolving Loans	22,875
Total loan outstanding	112,209	227,790
CFC | Distribution
Credit Quality
Total loan outstanding	25,437,077	23,844,242
CFC | Distribution | Pass
Credit Quality
2023	2,453,999
2022	2,404,404
2021	1,643,838
2020	1,822,745
2019	1,153,864
Prior	13,838,304
Revolving Loans	1,925,554
Total loan outstanding	25,242,708	23,596,004
CFC | Distribution | Special Mention
Credit Quality
2023	4,226
2022	0
2021	4,775
2020	0
2019	5,003
Prior	12,210
Revolving Loans	168,155
Total loan outstanding	194,369	248,238
CFC | Power supply
Credit Quality
Total loan outstanding	5,437,242	4,901,770
CFC | Power supply | Pass
Credit Quality
2023	465,638
2022	348,333
2021	547,897
2020	179,150
2019	375,738
Prior	2,687,787
Revolving Loans	720,490
Total loan outstanding	5,325,033	4,673,980
CFC | Power supply | Special Mention
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	0
Revolving Loans	0
Total loan outstanding	0	0
CFC | Power supply | Substandard
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	0
Revolving Loans	0
Total loan outstanding	0	0
CFC | Power supply | Doubtful
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	89,334
Revolving Loans	22,875
Total loan outstanding	112,209	227,790
CFC | Statewide and associate
Credit Quality
Total loan outstanding	200,368	126,863
CFC | Statewide and associate | Pass
Credit Quality
2023	61,671
2022	23,538
2021	1,938
2020	14,732
2019	2,863
Prior	16,418
Revolving Loans	66,150
Total loan outstanding	187,310	112,610
CFC | Statewide and associate | Special Mention
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	4,755
Prior	8,303
Revolving Loans	0
Total loan outstanding	13,058	14,253
NCSC
Credit Quality
Total loan outstanding	956,874	710,878
NCSC | Pass
Credit Quality
2023	268,157
2022	24,066
2021	5,678
2020	193,267
2019	3,741
Prior	274,826
Revolving Loans	187,139
Total loan outstanding	956,874	710,878
RTFC
Credit Quality
Total loan outstanding	487,788	467,601
RTFC | Pass
Credit Quality
2023	52,015
2022	84,624
2021	75,057
2020	39,157
2019	7,825
Prior	192,543
Revolving Loans	32,975
Total loan outstanding	484,196	463,509
RTFC | Special Mention
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	3,592
Revolving Loans	0
Total loan outstanding	3,592	4,092
RTFC | Doubtful
Credit Quality
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	0
Revolving Loans	0
Total loan outstanding	$ 0	$ 0