Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Before Tax:
Net other comprehensive income (loss)		$ 8			$ (1)			$ 17	$ 38
Tax Effect:
Net other comprehensive income (loss)		0			6			(3)	(20)
Net of Tax:
Net other comprehensive income (loss)		8	$ 7	$ (1)	5	$ (1)	$ 14	14	18
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		5			16			3	(12)
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		5			16			3	(12)
Tax Effect:
Net gain (loss)		1			2			0	(9)
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		1			2			0	(9)
Net of Tax:
Net gain (loss)		6			18			3	(21)
Reclassification to earnings		0			0			0	0
Net other comprehensive income (loss)		6			18			3	(21)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Before Tax:
Net gain (loss)		4			(5)			17	51
Reclassification to earnings	[1]	(5)			(5)			(16)	(3)
Net other comprehensive income (loss)		(1)			(10)			1	48
Tax Effect:
Net gain (loss)		(1)			1			(4)	(12)
Reclassification to earnings	[1]	1			1			4	1
Net other comprehensive income (loss)		0			2			0	(11)
Net of Tax:
Net gain (loss)		3			(4)			13	39
Reclassification to earnings	[1]	(4)			(4)			(12)	(2)
Net other comprehensive income (loss)		(1)			(8)			1	37
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		0			(25)			0	(25)
Reclassification to earnings	[2]	4			18			13	27
Net other comprehensive income (loss)		4			(7)			13	2
Tax Effect:
Net gain (loss)		0			6			0	6
Reclassification to earnings	[2]	(1)			(4)			(3)	(6)
Net other comprehensive income (loss)		(1)			2			(3)	0
Net of Tax:
Net gain (loss)		0			(19)			0	(19)
Reclassification to earnings	[2]	3			14			10	21
Net other comprehensive income (loss)		$ 3			$ (5)			$ 10	$ 2

[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.