Income Taxes (Loss Carryforwards) (Details) - USD ($) $ in Millions		Apr. 30, 2019		Apr. 30, 2018
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other		$ 54	[1]	$ 41
Deferred Tax Assets, Other Loss Carryforwards		9		8
Other Loss Carryforwards, Valuation Allowance		(6)		(7)
Loss Carryforwards		296		246
Deferred Tax Assets, Loss and Credit Carryforwards		55		51
Valuation Allowance		(25)		(29)
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss and Credit Carryforwards		68		34
Deferred Tax Assets, Operating Loss and Credit Carryforwards		6	[2]	2
Operating Loss and Credit Carryforwards, Valuation Allowance		0		0
Not Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss and Credit Carryforwards	[2]	0
Loss Carryforwards, Other		32
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | Brazil [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		42		48
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		14		16
Operating Loss Carryforwards, Valuation Allowance		(14)		(16)
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Non-trading Loss Carryforwards		27		29
Deferred Tax Assets, Non-Trading Loss Carryforwards		5		6
Non-trading Loss Carryforwards, Valuation Allowance		(5)		(6)
Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss and Credit Carryforwards	[2]	4
Loss Carryforwards, Other		22
Subject to Expiration [Member] | Foreign Tax Authority [Member] | FINLAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		105		94
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		21		19
Operating Loss Carryforwards, Valuation Allowance		$ 0		$ 0

[1] As of April 30, 2019, the gross amount includes loss carryforwards of $32 that do not expire and $22 that expire in varying amounts over the next 10 years.

[2] As of April 30, 2019, the net deferred tax asset amount includes credit carryforwards of $2 that do not expire and loss and credit carryforwards of $4 that expire in varying amounts from 2023 to 2039.