Pension and Other Postretirement Benefits (Textual) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution to benefit plans in 2016	$ 24
Estimated amount of prior service cost that will be amortized from accumulated other comprehensive loss into pension expense in 2016	1
Estimated amount of net actuarial loss that will be amortized from accumulated other comprehensive loss into pension expense in 2016	27
Medical and Life Insurance Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution to benefit plans in 2016	3
Estimated amount of prior service cost that will be amortized from accumulated other comprehensive loss into pension expense in 2016	3
Estimated amount of net actuarial loss that will be amortized from accumulated other comprehensive loss into pension expense in 2016	1
Project health care cost trend rates to decline gradually to, by 2023 and thereafter	5.00%
1% increase in assumed health care cost trend rates would have increased the accumulated postretirement benefit obligation	1
1% increase in assumed health care cost trend rates would have increased the aggregate service and interest costs	0
1% decrease in assumed health care cost trend rates would have decreased the accumulated postretirement benefit obligation	1
1% decrease in assumed health care cost trend rates would have decreased the aggregate service and interest costs	$ 0