Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Jan. 31, 2019	Jan. 31, 2018
Before Tax:
Net other comprehensive income (loss)		$ (1)			$ (21)			$ 38	$ (34)
Tax Effect:
Net other comprehensive income (loss)		6			30			(20)	42
Net of Tax:
Net other comprehensive income (loss)		5	$ (1)	$ 14	9	$ (15)	$ 14	18	8
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		16			24			(12)	27
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		16			24			(12)	27
Tax Effect:
Net gain (loss)		2			14			(9)	20
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		2			14			(9)	20
Net of Tax:
Net gain (loss)		18			38			(21)	47
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		18			38			(21)	47
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Before Tax:
Net gain (loss)		(5)			(51)			51	(80)
Reclassification to earnings	[1]	(5)			1			(3)	4
Net other comprehensive income (loss)		(10)			(50)			48	(76)
Tax Effect:
Net gain (loss)		1			18			(12)	29
Reclassification to earnings	[1]	1			0			1	(1)
Net other comprehensive income (loss)		2			18			(11)	28
Net of Tax:
Net gain (loss)		(4)			(33)			39	(51)
Reclassification to earnings	[1]	(4)			1			(2)	3
Net other comprehensive income (loss)		(8)			(32)			37	(48)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		(25)			0			(25)	0
Reclassification to earnings	[2]	18			5			27	15
Net other comprehensive income (loss)		(7)			5			2	15
Tax Effect:
Net gain (loss)		6			0			6	0
Reclassification to earnings	[2]	(4)			(2)			(6)	(6)
Net other comprehensive income (loss)		2			(2)			0	(6)
Net of Tax:
Net gain (loss)		(19)			0			(19)	0
Reclassification to earnings	[2]	14			3			21	9
Net other comprehensive income (loss)		$ (5)			$ 3			$ 2	$ 9

[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.