Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017	May 31, 2017	May 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Interest income	$ 20,000,000	$ 13,000,000	$ 40,000,000	$ 24,000,000
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	582,000,000		582,000,000
Available-for-sale securities with maturity dates over one year and less than five years from purchase date	36,000,000		36,000,000
Fair Value Measurements Using Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of long term debt	$ 3,171,000,000		$ 3,171,000,000			$ 3,294,000,000