Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		$ 8,190.9	$ 7,970.5	$ 7,891.1
Balance		8,124.8	8,190.9	7,970.5
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(50.5)	(35.5)	(16.4)
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		41.5	(15.0)	(19.1)
Income tax benefit (expense)		0.0	0.0	0.0
Balance		(9.0)	(50.5)	(35.5)
Net Gains (Losses) on Cash Flow Hedging Derivatives [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	[1]	(185.6)	(40.4)	(2.9)
Reclassification adjustments	[1]	13.8	2.1	0.4
Current period credit (charge)	[1]	0.0	(190.7)	(49.1)
Income tax benefit (expense)	[1]	(3.0)	43.4	11.2
Balance	[1]	(174.8)	(185.6)	(40.4)
Pension and Other Postretirement Liabilities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	[2]	(146.7)	(110.0)	(101.0)
Reclassification adjustments	[2]	46.3	7.4	7.3
Current period credit (charge)	[2]	18.9	(54.8)	(19.1)
Income tax benefit (expense)	[2]	(15.8)	10.7	2.8
Balance	[2]	(97.3)	(146.7)	(110.0)
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		3.8	4.1	3.6
Reclassification adjustments		0.0	0.0	0.0
Current period credit (charge)		(0.1)	(0.4)	0.7
Income tax benefit (expense)		0.0	0.1	(0.2)
Balance		3.7	3.8	4.1
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(379.0)	(181.8)	(116.7)
Reclassification adjustments		60.1	9.5	7.7
Current period credit (charge)		60.3	(260.9)	(86.6)
Income tax benefit (expense)		(18.8)	54.2	13.8
Balance		$ (277.4)	$ (379.0)	$ (181.8)

[1] 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. For additional information, see Note 10: 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 adjustments in 2021 primarily include the impact of the nonrecurring settlement charges related to the purchase of a group annuity contract to transfer our Canadian defined benefit pension plan obligations to an insurance company. For additional information, see Note 9: Pensions and Other Postretirement Benefits.