Income Taxes (Loss Carryforwards) (Details) - USD ($) $ in Millions	Apr. 30, 2018		Apr. 30, 2017
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other	$ 41	[1]	$ 43
Deferred Tax Assets, Other Loss Carryforwards	8		9
Other Loss Carryforwards, Valuation Allowance	(7)		(8)
Loss Carryforwards	246		184
Deferred Tax Assets, Loss Carryforwards	51		44
Valuation Allowance	(29)		(30)
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	34		0
Deferred Tax Assets, Operating Loss Carryforwards, State	2		0
Operating Loss Carryforwards, Valuation Allowance	0		0
Not Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other	11
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | Brazil [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	48		49
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	16		17
Operating Loss Carryforwards, Valuation Allowance	(16)		(17)
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Non-trading Loss Carryforwards	29		27
Deferred Tax Assets, Non-Trading Loss Carryforwards	6		5
Non-trading Loss Carryforwards, Valuation Allowance	(6)		(5)
Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other	30
Subject to Expiration [Member] | Foreign Tax Authority [Member] | FINLAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	94		65
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	19		13
Operating Loss Carryforwards, Valuation Allowance	$ 0		$ 0

[1] As of April 30, 2018, gross amount includes loss carryforwards of $11 that do not expire and $30 that expire in varying amounts over the next 10 years.