Income Taxes (Loss Carryforwards) (Details) - USD ($) $ in Millions		Apr. 30, 2020		Apr. 30, 2019
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other		$ 50	[1]	$ 54
Deferred Tax Assets, Other Loss Carryforwards		9		9
Other Loss Carryforwards, Valuation Allowance		(7)		(6)
Loss Carryforwards		289		296
Deferred Tax Assets, Loss and Credit Carryforwards		57		55
Valuation Allowance		(22)		(25)
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss and Credit Carryforwards		63		68
Deferred Tax Assets, Operating Loss and Credit Carryforwards		9	[2]	6
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]	3
Loss Carryforwards, Other		24
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | Brazil [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		31		42
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		10		14
Operating Loss Carryforwards, Valuation Allowance		(10)		(14)
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | United Kingdom
Operating Loss Carryforwards [Line Items]
Non-trading Loss Carryforwards		26		27
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]	6
Loss Carryforwards, Other		26
Subject to Expiration [Member] | Foreign Tax Authority [Member] | FINLAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		119		105
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		24		21
Operating Loss Carryforwards, Valuation Allowance		$ 0		$ 0

[1] As of April 30, 2020, the gross amount includes loss carryforwards of $24 that do not expire and $26 that expire in varying amounts over the next 20 years.

[2] As of April 30, 2020, the net deferred tax asset amount includes credit carryforwards of $3 that do not expire and loss and credit carryforwards of $6 that expire in varying amounts from 2023 to 2040.