Loans and Commitments (Details 4) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013	Aug. 31, 2012
Credit Quality
Total loans outstanding	$ 20,405,091	$ 20,296,317	$ 19,467,736
CFC
Credit Quality
Total loans outstanding	19,220,289	19,019,817
CFC | Distribution
Credit Quality
Total loans outstanding	15,083,474	14,941,192
CFC | Power supply
Credit Quality
Total loans outstanding	4,065,241	4,007,669
CFC | Statewide and associate
Credit Quality
Total loans outstanding	71,574	70,956
RTFC
Credit Quality
Total loans outstanding	479,769	503,359
NCSC
Credit Quality
Total loans outstanding	705,033	773,141
Pass
Credit Quality
Total loans outstanding	20,358,580	20,249,372
Pass | CFC
Credit Quality
Total loans outstanding	19,197,964	18,995,895
Pass | CFC | Distribution
Credit Quality
Total loans outstanding	15,066,434	14,922,558
Pass | CFC | Power supply
Credit Quality
Total loans outstanding	4,060,241	4,002,669
Pass | CFC | Statewide and associate
Credit Quality
Total loans outstanding	71,289	70,668
Pass | RTFC
Credit Quality
Total loans outstanding	460,043	483,058
Pass | NCSC
Credit Quality
Total loans outstanding	700,573	770,419
Criticized
Credit Quality
Total loans outstanding	46,511	46,945
Criticized | CFC
Credit Quality
Total loans outstanding	22,325	23,922
Criticized | CFC | Distribution
Credit Quality
Total loans outstanding	17,040	18,634
Criticized | CFC | Power supply
Credit Quality
Total loans outstanding	5,000	5,000
Criticized | CFC | Statewide and associate
Credit Quality
Total loans outstanding	285	288
Criticized | RTFC
Credit Quality
Total loans outstanding	19,726	20,301
Criticized | NCSC
Credit Quality
Total loans outstanding	$ 4,460	$ 2,722