Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other retirement plans income	$ 2	$ 27	$ 7	$ 80
Provision for income taxes		(7)	(1)	(19)
Net income	$ 2	$ 20	$ 6	$ 61