Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		$ 7,970.5	$ 7,891.1	$ 6,850.2
Reclassification of stranded tax effects	[1]			0.0
Balance		8,190.9	7,970.5	7,891.1
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(35.5)	(16.4)	(43.0)
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		(15.0)	(19.1)	26.6
Income tax benefit (expense)		0.0	0.0	0.0
Reclassification of stranded tax effects	[2]			0.0
Balance		(50.5)	(35.5)	(16.4)
Net Gains (Losses) on Cash Flow Hedging Derivatives [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	[3]	(40.4)	(2.9)	(4.4)
Reclassification adjustments	[3]	2.1	0.4	0.5
Current period credit (charge)	[3]	(190.7)	(49.1)	2.7
Income tax benefit (expense)	[3]	43.4	11.2	(1.2)
Reclassification of stranded tax effects	[2],[3]			(0.5)
Balance	[3]	(185.6)	(40.4)	(2.9)
Pension and Other Postretirement Liabilities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	[4]	(110.0)	(101.0)	(100.0)
Reclassification adjustments	[4]	7.4	7.3	10.7
Current period credit (charge)	[4]	(54.8)	(19.1)	9.2
Income tax benefit (expense)	[4]	10.7	2.8	(5.6)
Reclassification of stranded tax effects	[2],[4]			(15.3)
Balance	[4]	(146.7)	(110.0)	(101.0)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		4.1	3.6	4.0
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		(0.4)	0.7	(1.7)
Income tax benefit (expense)		0.1	(0.2)	0.5
Reclassification of stranded tax effects	[2]			0.8
Balance		3.8	4.1	3.6
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(181.8)	(116.7)	(143.4)
Reclassification adjustments		9.5	7.7	11.2
Current period credit (charge)		(260.9)	(86.6)	36.8
Income tax benefit (expense)		54.2	13.8	(6.3)
Reclassification of stranded tax effects	[1],[2]			(15.0)
Balance		$ (379.0)	$ (181.8)	$ (116.7)

[1] During 2018, we elected to early adopt Accounting Standards Update (“ASU”) 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220) Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allowed us to reclassify the stranded income tax effects resulting from the U.S. Tax Cuts and Jobs Act (the “Tax Act”) from accumulated other comprehensive income (loss) to retained earnings.

[2] During 2018, we adopted ASU 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220) Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allowed us to reclassify the stranded income tax effects resulting from the Tax Act from accumulated other comprehensive income (loss) to retained earnings.

[3] The reclassification from accumulated other comprehensive income (loss) to interest expense was related to terminated interest rate contracts. The current period charge in 2020 and 2019 relates to losses on the interest rate contracts entered into in November 2018 and June 2018 that were terminated in 2020. The current period credit in 2018 relates to the gain on the interest rate contract terminated in 2018. For additional information, see Note 10: Derivative Financial Instruments.

[4] Amortization of net losses and prior service costs was reclassified from accumulated other comprehensive income (loss) to other income (expense) – net.