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, 2014	Apr. 30, 2013	Apr. 30, 2012
Pension Benefits [Member]
Amounts recognized in OCI
Prior service credit (cost)	$ 0	$ (4)	$ (1)
Net actuarial gain (loss)	9	(18)	(102)
Amortization reclassified to earnings:
Prior service cost (credit)	1	1	1
Net actuarial loss (gain)	31	28	19
Net amount recognized in OCI	41	7	(83)
Medical and Life Insurance Benefits [Member]
Amounts recognized in OCI
Prior service credit (cost)	10	0	0
Net actuarial gain (loss)	(3)	(10)	(4)
Amortization reclassified to earnings:
Prior service cost (credit)	0	1	0
Net actuarial loss (gain)	0	0	0
Net amount recognized in OCI	$ 7	$ (9)	$ (4)