Derivative Instruments and Hedging Activities Derivatives Offsetting (Details) - USD ($) $ in Thousands	May 31, 2016	May 31, 2015
Derivative [Line Items]
Derivative assets	$ 80,095	$ 115,276
Derivative liabilities	594,820	408,382
Interest rate swaps
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	80,095	115,276
Derivative, Collateral, Obligation to Return Securities	80,095	115,276
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	594,820	408,382
Derivative, Collateral, Right to Reclaim Securities	80,095	115,276
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 514,725	$ 293,106