Loans - Schedule of loan portfolio by risk rating category and member class based on available data (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Credit Quality
2026	$ 3,152,482	$ 2,885,664
2025	2,750,825	3,257,380
2024	3,137,015	3,118,244
2023	3,021,027	2,637,319
2022	2,486,371	2,075,297
Prior	19,273,122	18,536,659
Revolving Loans	4,582,573	4,552,985
Total loans outstanding	38,403,415	37,063,548
Pass
Credit Quality
2026	3,151,919	2,885,664
2025	2,750,825	3,257,019
2024	3,136,658	3,114,118
2023	3,016,963	2,637,319
2022	2,486,371	2,070,729
Prior	19,236,674	18,483,883
Revolving Loans	4,417,438	4,396,053
Total loans outstanding	38,196,848	36,844,785
Special mention
Credit Quality
2026	563	0
2025	0	361
2024	357	4,126
2023	4,064	0
2022	0	4,568
Prior	28,948	26,677
Revolving Loans	165,135	156,932
Total loans outstanding	199,067	192,664
Substandard
Credit Quality
2026	0	0
2025	0	0
2024	0	0
2023	0	0
2022	0	0
Prior	0	0
Revolving Loans	0	0
Total loans outstanding	0	0
Doubtful
Credit Quality
2026	0	0
2025	0	0
2024	0	0
2023	0	0
2022	0	0
Prior	7,500	26,099
Revolving Loans	0	0
Total loans outstanding	7,500	26,099
Criticized
Credit Quality
2026	563	0
2025	0	361
2024	357	4,126
2023	4,064	0
2022	0	4,568
Prior	36,448	52,776
Revolving Loans	165,135	156,932
Total loans outstanding	206,567	218,763
CFC
Credit Quality
Total loans outstanding	36,747,017	35,409,320
CFC | Pass
Credit Quality
2026	2,918,827	2,751,833
2025	2,621,155	3,004,701
2024	2,933,823	2,822,866
2023	2,753,668	2,556,460
2022	2,444,002	2,016,700
Prior	18,698,934	17,902,012
Revolving Loans	4,170,041	4,136,585
Total loans outstanding	36,540,450	35,191,157
CFC | Special mention
Credit Quality
2026	563	0
2025	0	361
2024	357	4,126
2023	4,064	0
2022	0	4,568
Prior	28,948	26,677
Revolving Loans	165,135	156,332
Total loans outstanding	199,067	192,064
CFC | Distribution
Credit Quality
Total loans outstanding	30,085,224	29,262,495
CFC | Distribution | Pass
Credit Quality
2026	2,267,762	2,301,736
2025	2,179,606	2,471,765
2024	2,415,406	2,323,781
2023	2,269,673	2,256,706
2022	2,170,793	1,541,206
Prior	15,531,739	15,022,726
Revolving Loans	3,060,902	3,163,495
Total loans outstanding	29,895,881	29,081,415
CFC | Distribution | Special mention
Credit Quality
2026	563	0
2025	0	361
2024	357	4,126
2023	4,064	0
2022	0	4,568
Prior	19,224	15,693
Revolving Loans	165,135	156,332
Total loans outstanding	189,343	181,080
CFC | Power supply
Credit Quality
Total loans outstanding	6,403,396	5,895,500
CFC | Power supply | Pass
Credit Quality
2026	651,065	442,972
2025	435,159	496,642
2024	482,656	441,984
2023	429,479	296,948
2022	270,611	474,074
Prior	3,145,266	2,857,029
Revolving Loans	981,660	859,752
Total loans outstanding	6,395,896	5,869,401
CFC | Power supply | Doubtful
Credit Quality
2026	0	0
2025	0	0
2024	0	0
2023	0	0
2022	0	0
Prior	7,500	26,099
Revolving Loans	0	0
Total loans outstanding	7,500	26,099
CFC | Statewide and associate
Credit Quality
Total loans outstanding	258,397	251,325
CFC | Statewide and associate | Pass
Credit Quality
2026	0	7,125
2025	6,390	36,294
2024	35,761	57,101
2023	54,516	2,806
2022	2,598	1,420
Prior	21,929	22,257
Revolving Loans	127,479	113,338
Total loans outstanding	248,673	240,341
CFC | Statewide and associate | Special mention
Credit Quality
2026	0	0
2025	0	0
2024	0	0
2023	0	0
2022	0	0
Prior	9,724	10,984
Revolving Loans	0	0
Total loans outstanding	9,724	10,984
NCSC
Credit Quality
Total loans outstanding	1,656,398	1,654,228
NCSC | Pass
Credit Quality
2026	233,092	133,831
2025	129,670	252,318
2024	202,835	291,252
2023	263,295	80,859
2022	42,369	54,029
Prior	537,740	581,871
Revolving Loans	247,397	259,468
Total loans outstanding	1,656,398	1,653,628
NCSC | Electric
Credit Quality
Total loans outstanding	1,073,794	1,078,763
NCSC | Electric | Pass
Credit Quality
2026	122,588	81,315
2025	79,523	122,354
2024	90,059	250,610
2023	243,799	16,773
2022	15,907	4,131
Prior	324,006	385,564
Revolving Loans	197,912	217,416
Total loans outstanding	1,073,794	1,078,163
NCSC | Electric | Special mention
Credit Quality
2026		0
2025		0
2024		0
2023		0
2022		0
Prior		0
Revolving Loans		600
Total loans outstanding		600
NCSC | Telecom
Credit Quality
Total loans outstanding	582,604	575,465
NCSC | Telecom | Pass
Credit Quality
2026	110,504	52,516
2025	50,147	129,964
2024	112,776	40,642
2023	19,496	64,086
2022	26,462	49,898
Prior	213,734	196,307
Revolving Loans	49,485	42,052
Total loans outstanding	$ 582,604	$ 575,465