Changes in Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Jan. 31, 2014		Jan. 31, 2013	Jan. 31, 2014		Jan. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (201)			$ (211)
Other comprehensive income (loss) before reclassifications1	(8)	[1]		(7)	[2]
Amounts reclassified from AOCI	6			15
Net other comprehensive income (loss)	(14)		14	(19)		13
Net other comprehensive income (loss)	7		(2)	3		(3)
Net other comprehensive income (loss)	5		5	24		14
Net other comprehensive income (loss)	(2)		17	8		24
Ending balance	(203)			(203)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4)			0
Other comprehensive income (loss) before reclassifications1	6	[1]		3	[2]
Amounts reclassified from AOCI	1			0
Net other comprehensive income (loss)	7			3
Ending balance	3			3
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(4)			(2)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	5			10
Other comprehensive income (loss) before reclassifications1	(14)	[1]		(19)	[2]
Amounts reclassified from AOCI	0			0
Net other comprehensive income (loss)	(14)			(19)
Ending balance	(9)			(9)
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax	2			0
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(202)			(221)
Other comprehensive income (loss) before reclassifications1	0	[1]		9	[2]
Amounts reclassified from AOCI	5			15
Net other comprehensive income (loss)	5			24
Ending balance	(197)			(197)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	$ 0			$ (5)

[1] 1Net of tax benefit (cost) of $2, $(4), and $0 related to currency translation, cash flow hedges, and postretirement benefits, respectively.

[2] 1Net of tax benefit (cost) of $0, $(2), and $(5) related to currency translation, cash flow hedges, and postretirement benefits, respectively.