Pension and Other Postretirement Benefits (Changes in Funded Status of Benefit Plans Recognized in Other Comprehensive (Income) Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Pension Benefits [Member]
Amounts recognized in OCI
Prior service credit (cost)	$ 0	$ 0	$ (4)
Net actuarial gain (loss)	(80)	9	(18)
Amortization reclassified to earnings:
Prior service cost (credit)	1	1	1
Net actuarial loss (gain)	22	31	28
Net amount recognized in OCI	(57)	41	7
Medical and Life Insurance Benefits [Member]
Amounts recognized in OCI
Prior service credit (cost)	16	10	0
Net actuarial gain (loss)	(3)	(3)	(10)
Amortization reclassified to earnings:
Prior service cost (credit)	(2)	0	1
Net actuarial loss (gain)	1	0	0
Net amount recognized in OCI	$ 12	$ 7	$ (9)

Amount before tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit).

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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- Definition

Amount before tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

+ References+ Details