Retirement Benefits and Postemployment Benefits (Schedule of estimated benefit payments) (Details) $ in Millions	May 31, 2020 USD ($)
Defined Benefit Plan Estimated Future Benefit Payments [Abstract]
Medicare Subsidy Receipts, Next Twelve Months	$ 3.4
Medicare Subsidy Receipts, Year Two	3.7
Medicare Subsidy Receipts, Year Three	3.5
Medicare Subsidy Receipts, Year Four	2.8
Medicare Subsidy Receipts, Year Five	2.9
Medicare Subsidy Receipts, Five Fiscal Years Thereafter	14.4
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	325.4
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	331.8
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	338.6
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	345.9
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	354.5
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	1,899.7
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	43.5
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	44.5
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	45.6
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	46.7
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	48.0
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	247.0
Postemployment Benefit Plans [Member]
Defined Benefit Plan Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	24.5
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	19.6
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	18.1
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	16.8
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	15.6
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$ 63.6