Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Oct. 31, 2018	Jul. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Before Tax:
Net other comprehensive income (loss)		$ 12		$ (8)		$ 40	$ (13)
Tax Effect:
Net other comprehensive income (loss)		(13)		(7)		(27)	12
Net of Tax:
Net other comprehensive income (loss)		(1)	$ 14	(15)	$ 14	13	(1)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		(23)		(25)		(28)	3
Reclassification to earnings		0		0		0	0
Net other comprehensive income (loss)		(23)		(25)		(28)	3
Tax Effect:
Net gain (loss)		(4)		0		(11)	6
Reclassification to earnings		0		0		0	0
Net other comprehensive income (loss)		(4)		0		(11)	6
Net of Tax:
Net gain (loss)		(27)		(25)		(39)	9
Reclassification to earnings		0		0		0	0
Net other comprehensive income (loss)		(27)		(25)		(39)	9
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Before Tax:
Net gain (loss)		30		7		57	(29)
Reclassification to earnings	[1]	0		5		2	3
Net other comprehensive income (loss)		30		12		59	(26)
Tax Effect:
Net gain (loss)		(8)		(3)		(14)	11
Reclassification to earnings	[1]	0		(2)		0	(1)
Net other comprehensive income (loss)		(8)		(5)		(14)	10
Net of Tax:
Net gain (loss)		22		4		43	(18)
Reclassification to earnings	[1]	0		3		2	2
Net other comprehensive income (loss)		22		7		45	(16)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		0		(1)		0	0
Reclassification to earnings	[2]	5		6		9	10
Net other comprehensive income (loss)		5		5		9	10
Tax Effect:
Net gain (loss)		0		0		0	0
Reclassification to earnings	[2]	(1)		(2)		(2)	(4)
Net other comprehensive income (loss)		(1)		(2)		(2)	(4)
Net of Tax:
Net gain (loss)		0		(1)		0	0
Reclassification to earnings	[2]	4		4		7	6
Net other comprehensive income (loss)		$ 4		$ 3		$ 7	$ 6

[1] Pre-tax amount is classified as sales in the accompanying condensed consolidated statements of operations.

[2] Pre-tax amount is classified as non-operating postretirement expense in the accompanying condensed consolidated statements of operations.