Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Before Tax:
Net other comprehensive income (loss)		$ (21)	$ (28)	$ (34)	$ (55)
Tax Effect:
Net other comprehensive income (loss)		30	2	42	(28)
Net of Tax:
Net other comprehensive income (loss)		9	(26)	8	(83)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		24	(27)	27	(99)
Reclassification to earnings		0	0	0	0
Net other comprehensive income (loss)		24	(27)	27	(99)
Tax Effect:
Net gain (loss)		14	2	20	(11)
Reclassification to earnings		0	0	0	0
Net other comprehensive income (loss)		14	2	20	(11)
Net of Tax:
Net gain (loss)		38	(25)	47	(110)
Reclassification to earnings		0	0	0	0
Net other comprehensive income (loss)		38	(25)	47	(110)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Before Tax:
Net gain (loss)		(51)	5	(80)	57
Reclassification to earnings	[1]	1	(15)	4	(34)
Net other comprehensive income (loss)		(50)	(10)	(76)	23
Tax Effect:
Net gain (loss)		18	(3)	29	(23)
Reclassification to earnings	[1]	0	6	(1)	14
Net other comprehensive income (loss)		18	3	28	(9)
Net of Tax:
Net gain (loss)		(33)	2	(51)	34
Reclassification to earnings	[1]	1	(9)	3	(20)
Net other comprehensive income (loss)		(32)	(7)	(48)	14
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Before Tax:
Net gain (loss)		0	2	0	2
Reclassification to earnings	[2]	5	7	15	19
Net other comprehensive income (loss)		5	9	15	21
Tax Effect:
Net gain (loss)		0	(1)	0	(1)
Reclassification to earnings	[2]	(2)	(2)	(6)	(7)
Net other comprehensive income (loss)		(2)	(3)	(6)	(8)
Net of Tax:
Net gain (loss)		0	1	0	1
Reclassification to earnings	[2]	3	5	9	12
Net other comprehensive income (loss)		$ 3	$ 6	$ 9	$ 13

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

[2] Pre-tax amount is a component of pension and other postretirement benefit expense (as shown in Note 7, except for amounts related to non-U.S. benefit plans, about which no information is presented in Note 7 due to immateriality).