Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance		$ (237.4)
Accumulated Other Comprehensive Income (Loss), Ending Balance		(239.2)	$ (237.4)
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance		(21.1)	(9.0)	$ (50.5)
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		(13.2)	(12.1)	41.5
Income tax benefit (expense)		0.0	0.0	0.0
Accumulated Other Comprehensive Income (Loss), Ending Balance		(34.3)	(21.1)	(9.0)
Net Gains (Losses) on Cash Flow Hedging Derivatives [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	[1]	(163.9)	(174.8)	(185.6)
Reclassification adjustments	[1]	13.5	13.1	13.8
Current period credit (charge)	[1]	0.0	0.0	0.0
Income tax benefit (expense)	[1]	(3.2)	(2.2)	(3.0)
Accumulated Other Comprehensive Income (Loss), Ending Balance	[1]	(153.6)	(163.9)	(174.8)
Pension and Other Postretirement Liabilities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	[2]	(54.2)	(97.3)	(146.7)
Reclassification adjustments	[2]	10.3	17.6	46.3
Current period credit (charge)	[2]	(7.9)	38.1	18.9
Income tax benefit (expense)	[2]	(0.9)	(12.6)	(15.8)
Accumulated Other Comprehensive Income (Loss), Ending Balance	[2]	(52.7)	(54.2)	(97.3)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance		1.8	3.7	3.8
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		(0.6)	(2.5)	(0.1)
Income tax benefit (expense)		0.2	0.6	0.0
Accumulated Other Comprehensive Income (Loss), Ending Balance		1.4	1.8	3.7
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance		(237.4)	(277.4)	(379.0)
Reclassification adjustments		23.8	30.7	60.1
Current period credit (charge)		(21.7)	23.5	60.3
Income tax benefit (expense)		(3.9)	(14.2)	(18.8)
Accumulated Other Comprehensive Income (Loss), Ending Balance		$ (239.2)	$ (237.4)	$ (277.4)

[1] The reclassification from accumulated other comprehensive income (loss) is primarily composed of deferred gains (losses) related to terminated interest rate contracts which were reclassified to interest expense. For additional information, see Note 9: Derivative Financial Instruments.

[2] The reclassification from accumulated other comprehensive income (loss) to other income (expense) – net is composed of settlement charges and amortization of net losses and prior service costs. The reclassification in 2021 primarily includes the impact of the nonrecurring settlement charges related to the Canadian buy-out contract. For additional information, see Note 8: Pensions and Other Postretirement Benefits.