Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Statement of Other Comprehensive Income [Abstract]
Net income	$ 591	$ 513	$ 572
Other comprehensive income (loss), net of tax (cost) benefit:
Foreign currency translation adjustment, net of tax of $(9), $7, and $1 in 2011, 2012, and 2013, respectively	17	(55)	37
Amounts related to postretirement benefit plans:
Net actuarial gain (loss) and prior service cost, net of tax of $(9), $42, and $16 in 2011, 2012, and 2013, respectively	(16)	(67)	13
Reclassification to earnings, net of tax of $(8), $(8), and $(15) in 2011, 2012, and 2013, respectively	15	12	12
Amounts related to cash flow hedges:
Net (loss) gain on hedging instruments, net of tax of $10, $(3), and $(4) in 2011, 2012, and 2013, respectively	3	6	(17)
Reclassification to earnings, net of tax of $(3) in 2012 and $1 in 2013	0	5	0
Net other comprehensive income (loss)	19	(99)	45
Comprehensive income	$ 610	$ 414	$ 617