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Pension and Other Postretirement Benefits (Details 11)	12 Months Ended
Pension and Other Postretirement Benefits (Details 11)	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Pension Benefits [Member]
Assumptions used in computing benefit plan obligations
Discount rate	4.92%	5.67%
Rate of salary increase	4.00%	4.00%
Assumptions used in computing benefit plan expense
Discount rate	5.67%	5.91%	7.94%
Rate of salary increase	4.00%	4.00%	4.00%
Expected return on plan assets	8.25%	8.50%	8.50%
Medical and Life Insurance Benefits [Member]
Assumptions used in computing benefit plan obligations
Discount rate	4.84%	5.59%
Assumptions used in computing benefit plan expense
Discount rate	5.59%	5.78%	7.80%
Present rate before age 65 [Member] \| Medical and Life Insurance Benefits [Member]
Assumed health care cost trend rates
Present rate before age 65	8.00%	7.50%
Present rate age 65 and after [Member] \| Medical and Life Insurance Benefits [Member]
Assumed health care cost trend rates
Present rate before age 65	8.00%	7.50%

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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