Loans and Commitments (Details 4) - USD ($) $ in Thousands		Feb. 29, 2016		May. 31, 2015		Feb. 28, 2015
Credit Quality
Total loans outstanding		$ 23,134,215	[1],[2]	$ 21,459,220	[1],[2]	$ 21,202,399
CFC
Credit Quality
Total loans outstanding	[1]	22,079,012		20,341,990
CFC | Distribution
Credit Quality
Total loans outstanding	[1]	17,700,859		16,095,043
CFC | Power supply
Credit Quality
Total loans outstanding	[1]	4,322,069		4,181,481
CFC | Statewide and associate
Credit Quality
Total loans outstanding	[1]	56,084		65,466
RTFC
Credit Quality
Total loans outstanding	[1]	357,967		385,709
NCSC
Credit Quality
Total loans outstanding	[1]	697,236		731,521
Pass
Credit Quality
Total loans outstanding		23,084,929		21,409,443
Pass | CFC
Credit Quality
Total loans outstanding		22,045,775		20,309,197
Pass | CFC | Distribution
Credit Quality
Total loans outstanding		17,667,879		16,062,516
Pass | CFC | Power supply
Credit Quality
Total loans outstanding		4,322,069		4,181,481
Pass | CFC | Statewide and associate
Credit Quality
Total loans outstanding		55,827		65,200
Pass | RTFC
Credit Quality
Total loans outstanding		344,886		373,087
Pass | NCSC
Credit Quality
Total loans outstanding		694,268		727,159
Criticized
Credit Quality
Total loans outstanding		49,286		49,777
Criticized | CFC
Credit Quality
Total loans outstanding		33,237		32,793
Criticized | CFC | Distribution
Credit Quality
Total loans outstanding		32,980		32,527
Criticized | CFC | Power supply
Credit Quality
Total loans outstanding		0		0
Criticized | CFC | Statewide and associate
Credit Quality
Total loans outstanding		257		266
Criticized | RTFC
Credit Quality
Total loans outstanding		13,081		12,622
Criticized | NCSC
Credit Quality
Total loans outstanding		$ 2,968		$ 4,362

[1] Includes nonperforming and restructured loans.

[2] Represents the unpaid principal balance excluding deferred loan origination costs.