Derivative Instruments and Hedging Activities Derivatives - Income Statement Impact (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Derivative [Line Items]
Derivative cash settlements expense	[1],[2]	$ (207,871)	$ (204,166)	$ (421,142)	$ (414,397)
Derivative forward value gains (losses)				(187,082)	95,160
Derivative gains (losses)		183,450	63,343	(212,275)	70,526
Interest Rate Swap
Derivative [Line Items]
Derivative cash settlements expense		(14,150)	(11,805)	(25,193)	(24,634)
Derivative forward value gains (losses)		197,600	75,148	(187,082)	95,160
Derivative gains (losses)		$ 183,450	$ 63,343	$ (212,275)	$ 70,526

[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] 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.