Financing Arrangements - Additional Information (Details) - USD ($)	3 Months Ended
	Aug. 31, 2017	May 31, 2017
Line Of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date	Nov. 13, 2020
Letter of Credit Maximum Sublimit Amount	$ 500,000,000
Financial Covenant Terms Ratio	350.00%
Financial Covenant Compliance Ratio	190.00%
Letters Of Credit Outstanding	$ 317,000,000
Commercial paper outstanding	0
Letter of Credit Outstanding Sublimit Unused Amount	183,000,000
Long Term Debt Exclusive of Capital Leases Carrying Value	15,100,000,000	$ 14,900,000,000
Long Term Debt Exclusive Of Capital Leases Fair Value	$ 15,900,000,000	$ 15,500,000,000
Long-term debt weighted average interest rate	3.60%
Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Line of Credit Facility, Term	5 years
Line Of Credit Facility Maximum Borrowing Capacity	$ 1,750,000,000