Income Taxes (Operating Loss Carryforwards) (Details) - USD ($) $ in Millions	Apr. 30, 2017	Apr. 30, 2016
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 30	$ 25
Loss Carryforwards, Various, Valuation Allowance	8	7
Loss Carryforwards, Various	43
Not Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Various, Valuation Allowance	2
Loss Carryforwards, Various	14
Not Subject to Expiration [Member] | Brazil [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses in Brazil, valuation allowance	17	12
Net operating losses	49
Not Subject to Expiration [Member] | UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Non-trading loss carryforward, valuation allowance	5	$ 6
Non-trading loss carryforward	27
Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Various, Valuation Allowance	6
Loss Carryforwards, Various	29
Subject to Expiration [Member] | FINLAND
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 65