Summary of Significant Accounting Policies Interest Expense (Details) - USD ($) $ in Thousands		12 Months Ended
		May 31, 2019	May 31, 2018	May 31, 2017
Interest expense on debt:
Total interest expense	[1],[2]	$ 836,209	$ 792,735	$ 741,738
Short-term borrowings
Interest expense on debt:
Interest expense on debt	[1],[2]	92,854	50,616	26,684
Medium-term notes
Interest expense on debt:
Interest expense on debt	[1],[2]	133,797	111,814	99,022
Collateral trust bonds
Interest expense on debt:
Interest expense on debt	[1],[2]	273,413	336,079	340,854
Guaranteed Underwriter Program Notes Payable
Interest expense on debt:
Interest expense on debt		147,895	140,551	142,661
Farmer Mac Notes Payable
Interest expense on debt:
Interest expense on debt	[1],[2]	90,942	56,004	33,488
Long-term notes payable
Interest expense on debt:
Interest expense on debt	[1],[2]	1,237	1,509	1,780
Subordinated deferrable debt
Interest expense on debt:
Interest expense on debt	[1],[2]	38,628	37,661	37,657
Subordinated certificates
Interest expense on debt:
Interest expense on debt	[1],[2]	$ 57,443	$ 58,501	$ 59,592

[1] (1) Includes amortization of debt discounts and debt issuance costs, which are generally deferred and recognized as interest expense using the effective interest method. Issuance costs related to dealer commercial paper, however, are recognized as interest expense immediately as incurred.

[2] (2) Includes fees related to funding arrangements, such as up-front fees paid to banks participating in our committed bank revolving line of credit agreements. Depending on the nature of the fee, amounts may be deferred and recognized as interest expense ratably over the term of the arrangement or recognized immediately as incurred.