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Long-Term Debt (Narrative) (Details)
Oct. 31, 2018
USD ($)
Apr. 30, 2018
USD ($)
Oct. 31, 2017
USD ($)
Line of Credit Facility [Line Items]      
Outstanding balance under the 2017 CLOC $ 0    
Full borrowing capacity amount 1,700,000,000    
Estimated fair value of long-term debt 1,500,000,000 $ 1,500,000,000 $ 1,600,000,000
Revolving credit facility      
Line of Credit Facility [Line Items]      
Aggregate principal amount 2,000,000,000.0    
Available increase in borrowing capacity $ 500,000,000.0    
Maximum quarterly debt-to-EBITDA ratio 3.50    
Maximum annual debt-to-EBITDA ratio 4.50    
Minimum interest coverage ratio 2.50    
Swingline loans      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 200,000,000.0    
Standby letters of credit      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 50,000,000.0