Loans - Internal Risk Rating (Details) - USD ($) $ in Thousands	Nov. 30, 2019	May 31, 2019	Nov. 30, 2018
Credit Quality
Loans Outstanding	$ 26,426,879	$ 25,905,664	$ 25,282,953
CFC
Credit Quality
Loans Outstanding	25,368,276	24,817,676
CFC | Distribution
Credit Quality
Loans Outstanding	20,682,596	20,155,266
CFC | Power supply
Credit Quality
Loans Outstanding	4,601,783	4,578,841
CFC | Statewide and associate
Credit Quality
Loans Outstanding	83,897	83,569
NCSC
Credit Quality
Loans Outstanding	702,279	742,888
RTFC
Credit Quality
Loans Outstanding	356,324	345,100
Pass
Credit Quality
Loans Outstanding	26,227,586	25,703,866
Pass | CFC
Credit Quality
Loans Outstanding	25,174,325	24,621,470
Pass | CFC | Distribution
Credit Quality
Loans Outstanding	20,552,574	20,022,193
Pass | CFC | Power supply
Credit Quality
Loans Outstanding	4,554,111	4,530,708
Pass | CFC | Statewide and associate
Credit Quality
Loans Outstanding	67,640	68,569
Pass | NCSC
Credit Quality
Loans Outstanding	702,279	742,888
Pass | RTFC
Credit Quality
Loans Outstanding	350,982	339,508
Special Mention
Credit Quality
Loans Outstanding	25,820	25,375
Special Mention | CFC
Credit Quality
Loans Outstanding	25,820	25,375
Special Mention | CFC | Distribution
Credit Quality
Loans Outstanding	9,563	10,375
Special Mention | CFC | Statewide and associate
Credit Quality
Loans Outstanding	16,257	15,000
Special Mention | NCSC
Credit Quality
Loans Outstanding	0
Special Mention | RTFC
Credit Quality
Loans Outstanding	0	0
Substandard
Credit Quality
Loans Outstanding	173,473	176,423
Substandard | CFC
Credit Quality
Loans Outstanding	168,131	170,831
Substandard | CFC | Distribution
Credit Quality
Loans Outstanding	120,459	122,698
Substandard | CFC | Power supply
Credit Quality
Loans Outstanding	47,672	48,133
Substandard | RTFC
Credit Quality
Loans Outstanding	$ 5,342	$ 5,592