Loans - Schedule of Loans Outstanding by Borrower Risk Ratings and Origination Year (Details) - USD ($) $ in Thousands	Feb. 28, 2026	May 31, 2025	Feb. 28, 2025
Credit Quality
Term loans by fiscal year of origination, year one	$ 2,378,379	$ 2,885,664
Term loans by fiscal year of origination, year two	2,778,449	3,257,380
Term loans by fiscal year of origination, year three	3,187,010	3,118,244
Term loans by fiscal year of origination, year four	3,049,421	2,637,319
Term loans by fiscal year of origination, year five	2,542,034	2,075,297
Prior	19,649,112	18,536,659
Revolving Loans	5,147,274	4,552,985
Total	38,731,679	37,063,548	$ 36,463,440
CFC:
Credit Quality
Total	36,949,300	35,409,320
CFC: | Distribution
Credit Quality
Total	30,387,286	29,262,495
CFC: | Power supply
Credit Quality
Total	6,288,837	5,895,500
CFC: | Statewide and associate
Credit Quality
Total	273,177	251,325
NCSC:
Credit Quality
Total	1,782,379	1,654,228
NCSC: | Electric
Credit Quality
Total	1,163,391	1,078,763
NCSC: | Telecom
Credit Quality
Total	618,988	575,465
Pass
Credit Quality
Term loans by fiscal year of origination, year one	2,377,812	2,885,664
Term loans by fiscal year of origination, year two	2,778,449	3,257,019
Term loans by fiscal year of origination, year three	3,186,652	3,114,118
Term loans by fiscal year of origination, year four	3,045,341	2,637,319
Term loans by fiscal year of origination, year five	2,542,034	2,070,729
Prior	19,606,697	18,483,883
Revolving Loans	4,970,251	4,396,053
Total	38,507,236	36,844,785
Pass | CFC:
Credit Quality
Term loans by fiscal year of origination, year one	2,238,657	2,751,833
Term loans by fiscal year of origination, year two	2,647,889	3,004,701
Term loans by fiscal year of origination, year three	2,952,896	2,822,866
Term loans by fiscal year of origination, year four	2,770,816	2,556,460
Term loans by fiscal year of origination, year five	2,479,260	2,016,700
Prior	19,034,715	17,902,012
Revolving Loans	4,600,624	4,136,585
Total	36,724,857	35,191,157
Pass | CFC: | Distribution
Credit Quality
Term loans by fiscal year of origination, year one	1,741,279	2,301,736
Term loans by fiscal year of origination, year two	2,204,296	2,471,765
Term loans by fiscal year of origination, year three	2,430,939	2,323,781
Term loans by fiscal year of origination, year four	2,283,064	2,256,706
Term loans by fiscal year of origination, year five	2,199,096	1,541,206
Prior	15,815,662	15,022,726
Revolving Loans	3,511,438	3,163,495
Total	30,185,774	29,081,415
Pass | CFC: | Power supply
Credit Quality
Term loans by fiscal year of origination, year one	497,378	442,972
Term loans by fiscal year of origination, year two	437,079	496,642
Term loans by fiscal year of origination, year three	486,060	441,984
Term loans by fiscal year of origination, year four	432,577	296,948
Term loans by fiscal year of origination, year five	277,513	474,074
Prior	3,196,810	2,857,029
Revolving Loans	948,533	859,752
Total	6,275,950	5,869,401
Pass | CFC: | Statewide and associate
Credit Quality
Term loans by fiscal year of origination, year one	0	7,125
Term loans by fiscal year of origination, year two	6,514	36,294
Term loans by fiscal year of origination, year three	35,897	57,101
Term loans by fiscal year of origination, year four	55,175	2,806
Term loans by fiscal year of origination, year five	2,651	1,420
Prior	22,243	22,257
Revolving Loans	140,653	113,338
Total	263,133	240,341
Pass | NCSC:
Credit Quality
Term loans by fiscal year of origination, year one	139,155	133,831
Term loans by fiscal year of origination, year two	130,560	252,318
Term loans by fiscal year of origination, year three	233,756	291,252
Term loans by fiscal year of origination, year four	274,525	80,859
Term loans by fiscal year of origination, year five	62,774	54,029
Prior	571,982	581,871
Revolving Loans	369,627	259,468
Total	1,782,379	1,653,628
Pass | NCSC: | Electric
Credit Quality
Term loans by fiscal year of origination, year one	67,180	81,315
Term loans by fiscal year of origination, year two	79,836	122,354
Term loans by fiscal year of origination, year three	117,974	250,610
Term loans by fiscal year of origination, year four	243,939	16,773
Term loans by fiscal year of origination, year five	16,096	4,131
Prior	345,217	385,564
Revolving Loans	293,149	217,416
Total	1,163,391	1,078,163
Pass | NCSC: | Telecom
Credit Quality
Term loans by fiscal year of origination, year one	71,975	52,516
Term loans by fiscal year of origination, year two	50,724	129,964
Term loans by fiscal year of origination, year three	115,782	40,642
Term loans by fiscal year of origination, year four	30,586	64,086
Term loans by fiscal year of origination, year five	46,678	49,898
Prior	226,765	196,307
Revolving Loans	76,478	42,052
Total	618,988	575,465
Special mention
Credit Quality
Term loans by fiscal year of origination, year one	567	0
Term loans by fiscal year of origination, year two	0	361
Term loans by fiscal year of origination, year three	358	4,126
Term loans by fiscal year of origination, year four	4,080	0
Term loans by fiscal year of origination, year five	0	4,568
Prior	29,528	26,677
Revolving Loans	177,023	156,932
Total	211,556	192,664
Special mention | CFC:
Credit Quality
Term loans by fiscal year of origination, year one	567	0
Term loans by fiscal year of origination, year two	0	361
Term loans by fiscal year of origination, year three	358	4,126
Term loans by fiscal year of origination, year four	4,080	0
Term loans by fiscal year of origination, year five	0	4,568
Prior	29,528	26,677
Revolving Loans	177,023	156,332
Total	211,556	192,064
Special mention | CFC: | Distribution
Credit Quality
Term loans by fiscal year of origination, year one	567	0
Term loans by fiscal year of origination, year two	0	361
Term loans by fiscal year of origination, year three	358	4,126
Term loans by fiscal year of origination, year four	4,080	0
Term loans by fiscal year of origination, year five	0	4,568
Prior	19,484	15,693
Revolving Loans	177,023	156,332
Total	201,512	181,080
Special mention | CFC: | Statewide and associate
Credit Quality
Term loans by fiscal year of origination, year one	0	0
Term loans by fiscal year of origination, year two	0	0
Term loans by fiscal year of origination, year three	0	0
Term loans by fiscal year of origination, year four	0	0
Term loans by fiscal year of origination, year five	0	0
Prior	10,044	10,984
Revolving Loans	0	0
Total	10,044	10,984
Special mention | NCSC: | Electric
Credit Quality
Term loans by fiscal year of origination, year one		0
Term loans by fiscal year of origination, year two		0
Term loans by fiscal year of origination, year three		0
Term loans by fiscal year of origination, year four		0
Term loans by fiscal year of origination, year five		0
Prior		0
Revolving Loans		600
Total		600
Substandard
Credit Quality
Term loans by fiscal year of origination, year one	0	0
Term loans by fiscal year of origination, year two	0	0
Term loans by fiscal year of origination, year three	0	0
Term loans by fiscal year of origination, year four	0	0
Term loans by fiscal year of origination, year five	0	0
Prior	0	0
Revolving Loans	0	0
Total	0	0
Doubtful
Credit Quality
Term loans by fiscal year of origination, year one	0	0
Term loans by fiscal year of origination, year two	0	0
Term loans by fiscal year of origination, year three	0	0
Term loans by fiscal year of origination, year four	0	0
Term loans by fiscal year of origination, year five	0	0
Prior	12,887	26,099
Revolving Loans	0	0
Total	12,887	26,099
Doubtful | CFC: | Power supply
Credit Quality
Term loans by fiscal year of origination, year one	0	0
Term loans by fiscal year of origination, year two	0	0
Term loans by fiscal year of origination, year three	0	0
Term loans by fiscal year of origination, year four	0	0
Term loans by fiscal year of origination, year five	0	0
Prior	12,887	26,099
Revolving Loans	0	0
Total	12,887	26,099
Criticized
Credit Quality
Term loans by fiscal year of origination, year one	567	0
Term loans by fiscal year of origination, year two	0	361
Term loans by fiscal year of origination, year three	358	4,126
Term loans by fiscal year of origination, year four	4,080	0
Term loans by fiscal year of origination, year five	0	4,568
Prior	42,415	52,776
Revolving Loans	177,023	156,932
Total	$ 224,443	$ 218,763