Derivative Financial Instruments - Narrative (Details) - USD ($) shares in Millions, $ in Millions				12 Months Ended					70 Months Ended
		Nov. 15, 2023	Apr. 28, 2023	Apr. 30, 2024	Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2020	Apr. 30, 2015	Oct. 31, 2021
Derivative Financial Instruments (Textual) [Abstract]
Collateral received				$ 1.9
Collateral pledged					$ 17.0
Cumulative net mark-to-market valuation of certain derivative positions recognized in unallocated derivative gains (losses)				22.6	15.9
Settlement of interest rate contracts				42.5	0.0	$ 0.0
Interest expense – net				(264.3)	(152.0)	(160.9)
Other income (expense) – net	[1]			$ (25.6)	(14.7)	(19.1)
Amortization of deferred gain on early termination agreement						$ 4.0
Post Holdings Inc. | Pet Food Brands
Derivative Financial Instruments (Textual) [Abstract]
Proceeds from Divestiture of Business, Equity		5.4	5.4
Proceeds from investment in equity securities		$ 466.3
Commodity contracts
Derivative Financial Instruments (Textual) [Abstract]
Derivative instrument maturity				1 year
Foreign currency exchange contracts
Derivative Financial Instruments (Textual) [Abstract]
Derivative instrument maturity				1 year
Forward Contracts | Post Holdings Inc. | Pet Food Brands
Derivative Financial Instruments (Textual) [Abstract]
Gain (loss) on derivative - net				$ 5.4
Interest rate contract
Derivative Financial Instruments (Textual) [Abstract]
Settlement of interest rate contracts				42.5
Deferred pre-tax net gain (loss) included in accumulated other comprehensive loss							$ (239.8)
Deferred Gain (Loss) on Cash Flow Hedges Included in Accumulated Other Comprehensive Income or Loss				(187.1)	(200.7)
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive loss				44.0	$ 47.1
Effective portion of the hedge loss reclassified to interest expense over the next twelve months				$ (13.6)
Interest rate swap | Fair Value Hedging
Derivative Financial Instruments (Textual) [Abstract]
Amortization of deferred gain on early termination agreement									$ 53.5
Cash [Member] | Interest rate swap | Fair Value Hedging
Derivative Financial Instruments (Textual) [Abstract]
Gain (loss) on early termination agreement								$ 58.1
Accrued and Prepaid Interest Net | Interest rate swap | Fair Value Hedging
Derivative Financial Instruments (Textual) [Abstract]
Gain (loss) on early termination agreement								$ 4.6

[1] Includes special project costs related to certain divestiture, acquisition, integration, and restructuring activities. For more information, see Note 4: Special Project Costs and Note 8: Debt and Financing Arrangements.