Changes in Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jul. 31, 2013		Jul. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at April 30, 2013	$ (211)
Other comprehensive income (loss) before reclassifications (a)	(5)	[1]
Amounts reclassified from AOCI	4
Net other comprehensive income (loss)	(12)		(13)
Net other comprehensive income (loss)	6		8
Net other comprehensive income (loss)	(5)		(4)
Net other comprehensive income (loss)	(1)		(1)
Balance at July 31, 2013	(212)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at April 30, 2013	0
Other comprehensive income (loss) before reclassifications (a)	7	[1]
Amounts reclassified from AOCI	(1)
Net other comprehensive income (loss)	6
Balance at July 31, 2013	6
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(3)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at April 30, 2013	10
Other comprehensive income (loss) before reclassifications (a)	(12)	[1]
Amounts reclassified from AOCI	0
Net other comprehensive income (loss)	(12)
Balance at July 31, 2013	(2)
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax	0
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at April 30, 2013	(221)
Other comprehensive income (loss) before reclassifications (a)	0	[1]
Amounts reclassified from AOCI	5
Net other comprehensive income (loss)	(5)
Balance at July 31, 2013	(216)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	$ 0

[1] (a) Net of tax benefit (cost) of $0, $(3), and $0 related to currency translation adjustments, cash flow hedges, and postretirement benefits adjustments, respectively.