General - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	May 31, 2017	Jan. 26, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Gross contract assets related to in-transit packages	$ 513		$ 542
Contract assets net of deferred unearned revenue	351		363
Contract liabilities related to advance payments from customers	$ 15		$ 13
Payment terms of customer contracts	Under the typical payment terms of our customer contracts, the customer pays at periodic intervals (i.e., every 15 days, 30 days, 45 days, etc.) for shipments included on invoices received. It is not customary business practice to extend payment terms past 90 days, and as such, we do not have a practice of including a significant financing component within our revenue contracts with customers.
Stock-based compensation	$ 68	$ 62
Lease liability and related right-of-use asset	$ 13,000
Stock Repurchase Program Number Of Shares Authorized To Be Repurchased				25,000,000
Number of Shares Repurchased	2,600,000
Treasury Stock Acquired, Average Cost Per Share	$ 238.95
Payments for Repurchase of Common Stock	$ 625	$ 86
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	9,100,000
Dividends Payable, Date Declared	Aug. 17, 2018
Dividends Payable Amount Per Share	$ 0.65
Dividends Payable, Date To Be Paid	Oct. 01, 2018
Dividends Payable, Date Of Record	Sep. 10, 2018