Income Taxes (Loss Carryforwards) (Details) - USD ($)
$ in Millions
Apr. 30, 2021
Apr. 30, 2020
Operating Loss Carryforwards [Line Items]    
Loss Carryforwards, Other $ 64 [1] $ 50
Deferred Tax Assets, Other Loss Carryforwards 12 9
Other Loss Carryforwards, Valuation Allowance (10) (7)
Loss Carryforwards 327 289
Deferred Tax Assets, Loss and Credit Carryforwards 63 57
Valuation Allowance (20) (22)
State [Member]    
Operating Loss Carryforwards [Line Items]    
Operating Loss and Credit Carryforwards 91 63
Deferred Tax Assets, Operating Loss and Credit Carryforwards 13 [2] 9
Operating Loss and Credit Carryforwards, Valuation Allowance 5 0
Not Subject to Expiration [Member]    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Assets, Operating Loss and Credit Carryforwards [2] 5  
Loss Carryforwards, Other 29  
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | Brazil [Member]    
Operating Loss Carryforwards [Line Items]    
Operating Loss Carryforwards 30 31
Deferred Tax Assets, Operating Loss Carryforwards, Foreign 10 10
Operating Loss Carryforwards, Valuation Allowance 0 (10)
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | United Kingdom    
Operating Loss Carryforwards [Line Items]    
Non-trading Loss Carryforwards 29 26
Deferred Tax Assets, Non-Trading Loss Carryforwards 5 5
Non-trading Loss Carryforwards, Valuation Allowance (5) (5)
Subject to Expiration [Member]    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Assets, Operating Loss and Credit Carryforwards [2] 8  
Loss Carryforwards, Other 35  
Subject to Expiration [Member] | Foreign Tax Authority [Member] | FINLAND    
Operating Loss Carryforwards [Line Items]    
Operating Loss Carryforwards 113 119
Deferred Tax Assets, Operating Loss Carryforwards, Foreign 23 24
Operating Loss Carryforwards, Valuation Allowance $ 0 $ 0
[1] As of April 30, 2021, the gross amount includes loss carryforwards of $29 that do not expire and $35 that expire in varying amounts over the next 18 years.
[2] As of April 30, 2021, the net deferred tax asset amount includes credit carryforwards of $5 that do not expire and loss and credit carryforwards of $8 that expire in varying amounts from 2023 to 2041.