Income Taxes (Loss Carryforwards) (Details) - USD ($) $ in Millions		Apr. 30, 2021		Apr. 30, 2020
Operating Loss Carryforwards [Line Items]
Loss Carryforwards, Other		$ 64	[1]	$ 50
Deferred Tax Assets, Other Loss Carryforwards		12		9
Other Loss Carryforwards, Valuation Allowance		(10)		(7)
Loss Carryforwards		327		289
Deferred Tax Assets, Loss and Credit Carryforwards		63		57
Valuation Allowance		(20)		(22)
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss and Credit Carryforwards		91		63
Deferred Tax Assets, Operating Loss and Credit Carryforwards		13	[2]	9
Operating Loss and Credit Carryforwards, Valuation Allowance		5		0
Not Subject to Expiration [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss and Credit Carryforwards	[2]	5
Loss Carryforwards, Other		29
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | Brazil [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		30		31
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		10		10
Operating Loss Carryforwards, Valuation Allowance		0		(10)
Not Subject to Expiration [Member] | Foreign Tax Authority [Member] | United Kingdom
Operating Loss Carryforwards [Line Items]
Non-trading Loss Carryforwards		29		26
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]	8
Loss Carryforwards, Other		35
Subject to Expiration [Member] | Foreign Tax Authority [Member] | FINLAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		113		119
Deferred Tax Assets, Operating Loss Carryforwards, Foreign		23		24
Operating Loss Carryforwards, Valuation Allowance		$ 0		$ 0

[1] As of April 30, 2021, the gross amount includes loss carryforwards of $29 that do not expire and $35 that expire in varying amounts over the next 18 years.

[2] As of April 30, 2021, the net deferred tax asset amount includes credit carryforwards of $5 that do not expire and loss and credit carryforwards of $8 that expire in varying amounts from 2023 to 2041.