Pension and Other Postretirement Benefits (Change in Benefit Obligation) (Details) - USD ($) $ in Millions	12 Months Ended
Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Pension Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year	$ 903	$ 893
Service cost	24	24	$ 26
Interest cost	34	29	35
Net actuarial loss (gain)	28	2
Plan amendments	0	6
Retiree contributions	0	0
Benefits paid	(81)	(51)
Obligation at end of year	908	903	893
Medical and Life Insurance Benefits [Member]
Changes in present value of pension and other postretirement benefits
Obligation at beginning of year	50	52
Service cost	1	1	1
Interest cost	2	1	2
Net actuarial loss (gain)	0	1
Plan amendments	0	0
Retiree contributions	1	1
Benefits paid	(4)	(4)
Obligation at end of year	$ 50	$ 50	$ 52

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

+ References

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

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- Definition

Amount of contributions received by defined benefit plan from participant which increase benefit obligation.

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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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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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