Condensed Statements of Consolidated Shareholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Shares	Additional Capital	Retained Income	Accumulated Other Comprehensive Income (Loss)
Balance at Apr. 30, 2018	$ 7,891.1	$ 28.9	$ 5,739.7	$ 2,239.2	$ (116.7)
Balance, shares at Apr. 30, 2018		113,572,840
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	133.0			133.0
Other comprehensive income (loss)	(2.1)				(2.1)
Comprehensive Income	130.9
Purchase of treasury shares	(4.7)	$ 0.0	(4.6)	(0.1)
Purchase of treasury shares, shares		(43,913)
Stock plans	10.0	$ 0.0	10.0
Stock plans, shares		243,521
Cash dividends declared	(96.5)			(96.5)
Other	0.0			0.0
Balance at Jul. 31, 2018	7,930.8	$ 28.9	5,745.1	2,275.6	(118.8)
Balance, shares at Jul. 31, 2018		113,772,448
Balance at Apr. 30, 2018	7,891.1	$ 28.9	5,739.7	2,239.2	(116.7)
Balance, shares at Apr. 30, 2018		113,572,840
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	321.5
Other comprehensive income (loss)	0.3
Comprehensive Income	321.8
Balance at Oct. 31, 2018	8,030.0	$ 28.9	5,749.9	2,367.6	(116.4)
Balance, shares at Oct. 31, 2018		113,760,080
Balance at Jul. 31, 2018	7,930.8	$ 28.9	5,745.1	2,275.6	(118.8)
Balance, shares at Jul. 31, 2018		113,772,448
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	188.5			188.5
Other comprehensive income (loss)	2.4				2.4
Comprehensive Income	190.9
Purchase of treasury shares	(0.3)	$ 0.0	(0.3)	0.0
Purchase of treasury shares, shares		(2,485)
Stock plans	5.1	$ 0.0	5.1
Stock plans, shares		(9,883)
Cash dividends declared	(96.5)			(96.5)
Other	0.0	$ 0.0		0.0
Balance at Oct. 31, 2018	8,030.0	$ 28.9	5,749.9	2,367.6	(116.4)
Balance, shares at Oct. 31, 2018		113,760,080
Balance at Apr. 30, 2019	$ 7,970.5	$ 28.9	5,755.8	2,367.6	(181.8)
Balance, shares at Apr. 30, 2019	113,700,000	113,742,296
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 154.6			154.6
Other comprehensive income (loss)	(34.9)				(34.9)
Comprehensive Income	119.7
Purchase of treasury shares	(2.9)	$ 0.0	(2.7)	(0.2)
Purchase of treasury shares, shares		(22,793)
Stock plans	20.5	$ 0.1	20.4
Stock plans, shares		330,289
Cash dividends declared	(100.1)			(100.1)
Other	0.0			0.0
Balance at Jul. 31, 2019	8,007.7	$ 29.0	5,773.5	2,421.9	(216.7)
Balance, shares at Jul. 31, 2019		114,049,792
Balance at Apr. 30, 2019	$ 7,970.5	$ 28.9	5,755.8	2,367.6	(181.8)
Balance, shares at Apr. 30, 2019	113,700,000	113,742,296
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 365.8
Other comprehensive income (loss)	(66.6)
Comprehensive Income	299.2
Balance at Oct. 31, 2019	$ 8,095.3	$ 29.0	5,781.7	2,533.0	(248.4)
Balance, shares at Oct. 31, 2019	114,100,000	114,059,744
Balance at Jul. 31, 2019	$ 8,007.7	$ 29.0	5,773.5	2,421.9	(216.7)
Balance, shares at Jul. 31, 2019		114,049,792
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	211.2			211.2
Other comprehensive income (loss)	(31.7)				(31.7)
Comprehensive Income	179.5
Purchase of treasury shares	(0.6)	$ 0.0	(0.6)	0.0
Purchase of treasury shares, shares		(4,930)
Stock plans	8.8	$ 0.0	8.8
Stock plans, shares		14,882
Cash dividends declared	(100.1)			(100.1)
Other	0.0			0.0
Balance at Oct. 31, 2019	$ 8,095.3	$ 29.0	$ 5,781.7	$ 2,533.0	$ (248.4)
Balance, shares at Oct. 31, 2019	114,100,000	114,059,744