Income Taxes (Operating Loss Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 25	$ 24
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	75
Brazil [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses in Brazil, valuation allowance	13
UK Non Trading Loss [Member]
Operating Loss Carryforwards [Line Items]
Non-trading loss carryforward, valuation allowance	8
Not Subject to Expiration [Member] | Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Non-trading loss carryforward	36
Net operating losses	57
Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Foreign credit carryforward	6
Subject to Expiration [Member] | Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	18
Subject to Expiration [Member] | State [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 46