Income Taxes (Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 11	$ 11	$ 9
Additions for tax positions provided in prior periods	2	1	5
Additions for tax positions provided in current period	0	1	1
Decreases for tax positions provided in prior years	(1)	(2)	(4)
Settlements of tax positions in the current period	(1)	0	0
Unrecognized tax benefits at end of year	11	$ 11	$ 11
Unrecognized Tax Benefits [Abstract]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	9
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 0

Unrecognized Tax Benefits [Abstract]

No definition available.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

+ References

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- Definition

Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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