Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	May 31, 2017	May 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Interest income	$ 20,000,000	$ 11,000,000
Fair value transfers between fair value hierarchy levels	0		$ 0
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities with maturity dates within one year from purchase date	954,000,000
Available-for-sale securities with maturity dates over one year and less than five years from purchase date	33,000,000
Fair Value Measurements Using Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of long term debt	$ 3,301,000,000			$ 3,294,000,000