Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Apr. 30, 2019
SEC Schedule, 12-09, Allowance, Credit Loss [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period $ 11 $ 7 $ 7
Additions Charged to Costs and Expenses 0 4 1
Additions Charged to Other Accounts 0 0 0
Deductions 4 [1] 0 1 [1]
Balance at End of Period 7 11 7
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 22 25 29
Additions Charged to Costs and Expenses 10 2 1
Additions Charged to Other Accounts 0 0 1
Deductions 12 5 6
Balance at End of Period $ 20 $ 22 $ 25
[1] Doubtful accounts written off, net of recoveries.