Post (POST) 10-Q 7 May 21 2021 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Mar. 31, 2021	May 03, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-35305
Entity Registrant Name	Post Holdings, Inc.
Entity Incorporation, State or Country Code	MO
Entity Tax Identification Number	45-3355106
Entity Address, Address Line One	2503 S. Hanley Road
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63144
City Area Code	314
Local Phone Number	644-7600
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	POST
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		63,629,827
Entity Central Index Key	0001530950
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Net Sales	$ 1,483.3	$ 1,494.2	$ 2,941.3	$ 2,951
Cost of goods sold	1,032.3	1,055.4	2,034.9	2,040.7
Gross Profit	451	438.8	906.4	910.3
Selling, general and administrative expenses	249.4	245	500.5	480.3
Amortization of intangible assets	58.5	40	99.1	80.1
Other operating (income) expenses, net	(2)	0.3	(4.6)	0.4
Operating Profit	145.1	153.5	311.4	349.5
Interest expense, net	94.8	94	191.4	196.9
Loss on extinguishment and refinancing of debt, net	94.7	60	94.7	72.9
(Income) expense on swaps, net	(185.6)	224.6	(227.2)	163.2
Other income, net	(6.1)	(3.3)	(16.9)	(6.5)
Earnings (Loss) before Income Taxes and Equity Method Loss	147.3	(221.8)	269.4	(77)
Income tax expense (benefit)	29.5	(47.1)	52.7	(16.7)
Equity method loss, net of tax	7	11.1	14.9	18.4
Net Earnings (Loss) Including Noncontrolling Interests	110.8	(185.8)	201.8	(78.7)
Less: Net earnings attributable to noncontrolling interests	0.9	5.6	10.7	13.5
Net Earnings (Loss)	$ 109.9	$ (191.4)	$ 191.1	$ (92.2)
Earnings (Loss) per Share, Basic (in usd per share)	$ 1.71	$ (2.76)	$ 2.94	$ (1.32)
Earnings (Loss) per Share, Diluted (in usd per share)	$ 1.69	$ (2.76)	$ 2.90	$ (1.32)
Weighted-Average Common Shares Outstanding, Basic (in shares)	64.1	69.3	64.9	70
Weighted-Average Common Shares Outstanding, Diluted (in shares)	65.1	69.3	66	70

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net Earnings (Loss) Including Noncontrolling Interests	$ 110.8	$ (185.8)	$ 201.8	$ (78.7)
Pension and postretirement benefits adjustments:
Reclassifications to net earnings (loss)	(0.2)	(0.5)	(0.4)	(1)
Hedging adjustments:
Net gain on derivatives	0	55.8	0	22.5
Reclassifications to net earnings (loss)	0.6	(0.2)	1.1	7
Foreign currency translation adjustments:
Unrealized foreign currency translation adjustments	14	(109.5)	115.6	5.6
Tax benefit (expense) on pension and postretirement benefits adjustments:
Reclassifications to net earnings (loss)	0.1	0.1	0.2	0.2
Tax benefit (expense) on hedging adjustments:
Net gain on derivatives	0	(13.9)	0	(5.4)
Reclassifications to net earnings (loss)	(0.1)	0	(0.2)	(1.6)
Total Other Comprehensive Income (Loss) Including Noncontrolling Interests	14.4	(68.2)	116.3	27.3
Less: Comprehensive income attributable to noncontrolling interests	0.8	2.1	10.9	10.5
Total Comprehensive Income (Loss)	$ 124.4	$ (256.1)	$ 307.2	$ (61.9)

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
ASSETS
Cash and cash equivalents	$ 740.5	$ 1,187.9
Restricted cash	2.1	5.5
Receivables, net	554.8	441.6
Inventories	639.7	599.4
Prepaid expenses and other current assets	128.4	53.4
Total Current Assets	2,065.5	2,287.8
Property, net	1,776.6	1,779.7
Goodwill	4,574.6	4,438.6
Other intangible assets, net	3,214.2	3,197.5
Equity method investments	99.7	114.1
Other assets	410.4	329
Total Assets	12,141	12,146.7
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current portion of long-term debt	74.3	64.9
Accounts payable	406.5	367.9
Other current liabilities	409.3	541.6
Total Current Liabilities	890.1	974.4
Long-term debt	6,981	6,959
Deferred income taxes	858.5	784.5
Other liabilities	524.4	599.8
Total Liabilities	9,254	9,317.7
Common stock	0.8	0.8
Additional paid-in capital	4,237.7	4,182.9
Retained earnings	399.7	208.6
Accumulated other comprehensive income (loss)	86.8	(29.3)
Treasury stock, at cost	(1,823.8)	(1,508.5)
Total Shareholders’ Equity Excluding Noncontrolling Interests	2,901.2	2,854.5
Noncontrolling interests	(14.2)	(25.5)
Total Shareholders’ Equity	2,887	2,829
Total Liabilities and Shareholders’ Equity	$ 12,141	$ 12,146.7

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash Flows from Operating Activities:
Net Earnings (Loss) Including Noncontrolling Interests	$ 201.8	$ (78.7)
Adjustments to reconcile net earnings (loss) including noncontrolling interests to net cash provided by operating activities:
Depreciation and amortization	207.5	181.8
Unrealized (gain) loss on interest rate swaps and foreign exchange contracts, net	(242.5)	150.9
Loss on extinguishment and refinancing of debt, net	94.7	72.9
Non-cash stock-based compensation expense	27.7	24.7
Equity method loss, net of tax	14.9	18.4
Deferred income taxes	53.6	(58.6)
Other, net	(11.4)	5.5
Other changes in operating assets and liabilities, net of business acquisitions:
Increase in receivables, net	(104.1)	(90.4)
(Increase) decrease in inventories	(27.7)	9.9
Increase in prepaid expenses and other current assets	(41.7)	(23.2)
Increase in other assets	(9.1)	(16.9)
Decrease in accounts payable and other current liabilities	(16.4)	(111.1)
Increase in non-current liabilities	15	3.8
Net Cash Provided by Operating Activities	162.3	89
Cash Flows from Investing Activities:
Business acquisitions, net of cash acquired	(153.7)	0
Additions to property	(99.4)	(117.5)
Proceeds from sale of property and assets held for sale	18.7	2.4
Purchases of equity securities	(5)	0
Investments in partnerships	(17.1)	0
Cross-currency swap cash settlements	0	52.7
Net Cash Used in Investing Activities	(256.5)	(62.4)
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt	1,820	3,846
Repayments of long-term debt	(1,794.6)	(3,731.5)
Payments to appraisal rights holders	0	(3.8)
Purchases of treasury stock	(322.7)	(437.8)
Proceeds from initial public offering	0	524.4
Payments of debt issuance costs and deferred financing fees	(16.8)	(39.8)
Refund of debt issuance costs	0	15.3
Payments of debt premiums and refinancing fees	(75.8)	(49.8)
Cash received from share repurchase contracts	47.5	0
Other, net	(20.3)	(7.1)
Net Cash (Used in) Provided by Financing Activities	(362.7)	115.9
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	6.1	(0.4)
Net (Decrease) Increase in Cash, Cash Equivalents and Restricted Cash	(450.8)	142.1
Cash, Cash Equivalents and Restricted Cash, Beginning of Year	1,193.4	1,054.5
Cash, Cash Equivalents and Restricted Cash, End of Period	$ 742.6	$ 1,196.6

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Shareholders' Equity Statement - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Retirement Benefit Adjustments, net of tax	Hedging Adjustments, net of tax	Foreign Currency Translation Adjustments	Treasury Stock	Noncontrolling Interests
Shareholders' Equity Excluding Noncontrolling Interest, Beginning of period at Sep. 30, 2019		$ 0.8	$ 3,734.8	$ 207.8	$ 26.6	$ 44.5	$ (167.9)	$ (920.7)
Total Shareholders' Equity, Beginning of period at Sep. 30, 2019									$ 11.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	$ (92.2)			(92.2)
Activity under stock and deferred compensation plans			(7)						0
Distribution to noncontrolling interest									0
Non-cash stock-based compensation expense			23.6						1.1
Cash received from share repurchase contracts	0		0
Initial public offering			455.6						(64.9)
Purchases of treasury stock								(429.1)
Net earnings attributable to noncontrolling interests	13.5								13.5
Net change in retirement benefits, net of tax					(0.8)
Net change in hedges, net of tax						25.3			(2.8)
Foreign currency translation adjustments							5.8		(0.2)
Shareholders' Equity Excluding Noncontrolling Interest, End of period at Mar. 31, 2020	2,907.1	0.8	4,207	115.6	25.8	69.8	(162.1)	(1,349.8)
Total Shareholders' Equity, End of period at Mar. 31, 2020	2,865.2								(41.9)
Shareholders' Equity Excluding Noncontrolling Interest, Beginning of period at Dec. 31, 2019		0.8	4,195.6	307	26.2	25.1	(53.1)	(1,143.8)
Total Shareholders' Equity, Beginning of period at Dec. 31, 2019									(46.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	(191.4)			(191.4)
Activity under stock and deferred compensation plans			0.3						0
Distribution to noncontrolling interest									0
Non-cash stock-based compensation expense			12.5						0.8
Cash received from share repurchase contracts			0
Initial public offering			(1.4)						1.4
Purchases of treasury stock								(206)
Net earnings attributable to noncontrolling interests	5.6								5.6
Net change in retirement benefits, net of tax					(0.4)
Net change in hedges, net of tax						44.7			(3)
Foreign currency translation adjustments							(109)		(0.5)
Shareholders' Equity Excluding Noncontrolling Interest, End of period at Mar. 31, 2020	2,907.1	0.8	4,207	115.6	25.8	69.8	(162.1)	(1,349.8)
Total Shareholders' Equity, End of period at Mar. 31, 2020	2,865.2								(41.9)
Shareholders' Equity Excluding Noncontrolling Interest, Beginning of period at Sep. 30, 2020	2,854.5	0.8	4,182.9	208.6	(4.3)	70.3	(95.3)	(1,508.5)
Total Shareholders' Equity, Beginning of period at Sep. 30, 2020	2,829								(25.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	191.1			191.1
Activity under stock and deferred compensation plans			(18.2)						(0.8)
Distribution to noncontrolling interest									(1)
Non-cash stock-based compensation expense			25.5						2.2
Cash received from share repurchase contracts	47.5		47.5
Initial public offering			0						0
Purchases of treasury stock								(315.3)
Net earnings attributable to noncontrolling interests	10.7								10.7
Net change in retirement benefits, net of tax					(0.2)
Net change in hedges, net of tax						0.6			0.3
Foreign currency translation adjustments							115.7		(0.1)
Shareholders' Equity Excluding Noncontrolling Interest, End of period at Mar. 31, 2021	2,901.2	0.8	4,237.7	399.7	(4.5)	70.9	20.4	(1,823.8)
Total Shareholders' Equity, End of period at Mar. 31, 2021	2,887								(14.2)
Shareholders' Equity Excluding Noncontrolling Interest, Beginning of period at Dec. 31, 2020		0.8	4,226.2	289.8	(4.4)	70.6	6.1	(1,668.4)
Total Shareholders' Equity, Beginning of period at Dec. 31, 2020									(16.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	109.9			109.9
Activity under stock and deferred compensation plans			(1.2)						0.1
Distribution to noncontrolling interest									0
Non-cash stock-based compensation expense			12.7						1.1
Cash received from share repurchase contracts			0
Initial public offering			0						0
Purchases of treasury stock								(155.4)
Net earnings attributable to noncontrolling interests	0.9								0.9
Net change in retirement benefits, net of tax					(0.1)
Net change in hedges, net of tax						0.3			0.2
Foreign currency translation adjustments							14.3		(0.3)
Shareholders' Equity Excluding Noncontrolling Interest, End of period at Mar. 31, 2021	2,901.2	$ 0.8	$ 4,237.7	$ 399.7	$ (4.5)	$ 70.9	$ 20.4	$ (1,823.8)
Total Shareholders' Equity, End of period at Mar. 31, 2021	$ 2,887								$ (14.2)

Basis of Presentation

Basis of Presentation	6 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	BASIS OF PRESENTATIONThese unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”), under the rules and regulations of the United States (“U.S.”) Securities and Exchange Commission (the “SEC”), and on a basis substantially consistent with the audited consolidated financial statements of Post Holdings, Inc. (herein referred to as “Post,” “the Company,” “us,” “our” or “we,” and unless otherwise stated or context otherwise indicates, all such references herein mean Post Holdings, Inc. and its consolidated subsidiaries) as of and for the fiscal year ended September 30, 2020. These unaudited condensed consolidated financial statements should be read in conjunction with such audited consolidated financial statements, which are included in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2020, filed with the SEC on November 20, 2020. These unaudited condensed consolidated financial statements include all adjustments (consisting of normal recurring adjustments and accruals) that management considers necessary for a fair statement of the Company’s results of operations, comprehensive income, financial condition, cash flows and shareholders’ equity for the interim periods presented. Interim results are not necessarily indicative of the results for any other interim period or for the entire fiscal year.

Recently Issued and Adopted Acc

Recently Issued and Adopted Accounting Standards (Notes)	6 Months Ended
	Mar. 31, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
Recently Issued and Adopted Accounting Standards	RECENTLY ISSUED AND ADOPTED ACCOUNTING STANDARDS The Company has considered all new accounting pronouncements and has concluded there are no new pronouncements (other than the ones described below) that had or will have a material impact on the Company’s results of operations, comprehensive income, financial condition, cash flows, shareholders’ equity or disclosures based on current information. Recently Issued In March 2020, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” This ASU provides optional expedients and exceptions for contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. The expedients and exceptions provided by this ASU do not apply to contract modifications made and hedging relationships entered into or evaluated after December 31, 2022. This ASU is elective and effective for all entities as of March 12, 2020, the date this ASU was issued. An entity may elect to apply the amendments for contract modifications provided by this ASU as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or prospectively from a date within an interim period that includes or is subsequent to March 12, 2020. Once elected, this ASU must be applied prospectively for all eligible contract modifications. The Company is currently evaluating the impact of this ASU as it relates to its debt and hedging relationships. Recently Adopted

Noncontrolling Interests, Equit

Noncontrolling Interests, Equity Interests and Related Party Transactions (Notes)	6 Months Ended
	Mar. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Noncontrolling Interests, Equity Interests and Related Party Transactions	NONCONTROLLING INTERESTS, EQUITY INTERESTS AND RELATED PARTY TRANSACTIONS BellRing On October 21, 2019, BellRing Brands, Inc. (“BellRing”), a subsidiary of the Company, closed its initial public offering (the “BellRing IPO”) of 39.4 shares of its Class A common stock, $0.01 par value per share (the “Class A Common Stock”). BellRing received net proceeds from the BellRing IPO of $524.4, after deducting underwriting discounts and commissions. As a result of the BellRing IPO and certain other transactions completed in connection with the BellRing IPO, BellRing became a publicly-traded company whose Class A Common Stock is traded on the New York Stock Exchange under the ticker symbol “BRBR” and the holding company of BellRing Brands, LLC, a Delaware limited liability company (“BellRing LLC”), owning 28.8% of BellRing LLC’s non-voting membership units (the “BellRing LLC units”), with Post owning 71.2% of the BellRing LLC units and one share of BellRing’s Class B common stock, $0.01 par value per share (the “Class B Common Stock” and, collectively with the Class A Common Stock, the “BellRing Common Stock”). The Class B Common Stock has voting rights but no rights to dividends or other economic rights. For so long as Post or its affiliates (other than BellRing and its subsidiaries) directly own more than 50% of the BellRing LLC units, the Class B Common Stock represents 67% of the combined voting power of the BellRing Common Stock, which provides the Company control over BellRing’s board of directors and results in the full consolidation of BellRing and its subsidiaries into the Company’s financial statements. The BellRing LLC units held by the Company include a redemption feature that allows the Company to, at BellRing LLC’s option (as determined by its board of managers), redeem BellRing LLC units for either (i) Class A Common Stock of BellRing or (ii) cash equal to the market value of the BellRing Class A Common Stock at the time of redemption. BellRing LLC is the holding company for the Company’s historical active nutrition business. The term “BellRing” as used herein generally refers to BellRing Brands, Inc.; however, in discussions related to debt facilities, the term “BellRing” refers to BellRing Brands, LLC. BellRing and its subsidiaries are reported herein as the BellRing Brands segment. In the event the Company (other than BellRing and its subsidiaries) holds 50% or less of the BellRing LLC units, the holder of the share of Class B Common Stock will be entitled to a number of votes equal to the number of BellRing LLC units held by all persons other than BellRing and its subsidiaries. In such situation, the Company, as the holder of the share of Class B Common Stock, will only be entitled to cast a number of votes equal to the number of BellRing LLC units held by the Company (other than BellRing and its subsidiaries). Also, in such situation, if any BellRing LLC units are held by persons other than the Company, then the Company, as the holder of the share of Class B Common Stock, will cast the remainder of votes to which the share of Class B Common Stock is entitled only in accordance with the instructions and directions from such other holders of the BellRing LLC units. As of March 31, 2021 and September 30, 2020, the Company (other than BellRing and its subsidiaries) owned 71.2% of the BellRing LLC units and the net income and net assets of BellRing and its subsidiaries were consolidated within the Company’s financial statements, and the remaining 28.8% of the consolidated net income and net assets of BellRing and its subsidiaries, representing the percentage of economic interest in BellRing LLC held by BellRing (and therefore indirectly held by the public stockholders of BellRing through their ownership of the Class A Common Stock), were allocated to noncontrolling interest (“NCI”). The following table summarizes the effects of changes in ownership of BellRing on the Company’s equity: Three Months Ended Six Months Ended 2021 2020 2021 2020 Increase in additional paid-in capital related to net proceeds from BellRing IPO $ — $ — $ — $ 524.4 (Decrease) increase in additional paid-in capital related to establishment of noncontrolling interest — (1.4) — 64.9 Decrease in additional paid-in capital related to tax effects of BellRing IPO — — — (133.7) Net transfers (to) from NCI $ — $ (1.4) $ — $ 455.6 8th Avenue The Company has a 60.5% common equity interest in 8th Avenue Food & Provisions, Inc. (“8th Avenue”) that is accounted for using the equity method. In determining the accounting treatment of the common equity interest, management concluded that 8th Avenue was not a variable interest entity as defined by Accounting Standards Codification (“ASC”) Topic 810, “Consolidation” and, as such, was evaluated under the voting interest model. Based on the terms of 8th Avenue’s governing documents, management determined that the Company does not have a controlling voting interest in 8th Avenue due to substantive participating rights held by third parties associated with the governance of 8th Avenue. However, Post does retain significant influence, and therefore, the use of the equity method of accounting is required. The following table presents the calculation of the Company’s equity method loss attributable to 8th Avenue: Three Months Ended Six Months Ended 2021 2020 2021 2020 8th Avenue’s net loss available to 8th Avenue’s common shareholders $ (8.5) $ (15.2) $ (18.7) $ (23.9) 60.5 % 60.5 % 60.5 % 60.5 % Equity method loss available to Post $ (5.1) $ (9.2) $ (11.3) $ (14.5) Less: Amortization of basis difference, net of tax (a) 1.7 1.7 3.4 3.4 Equity method loss, net of tax $ (6.8) $ (10.9) $ (14.7) $ (17.9) (a) The Company adjusted the historical basis of 8th Avenue’s assets and liabilities to fair value and recognized a basis difference of $70.3. The basis difference related to property, plant and equipment and other intangible assets is being amortized over the weighted average useful lives of the assets. At March 31, 2021 and September 30, 2020, the remaining basis difference to be amortized was $51.2 and $54.6, respectively. Summarized financial information of 8th Avenue is presented in the following table. Three Months Ended Six Months Ended 2021 2020 2021 2020 Net sales $ 220.7 $ 233.1 $ 449.7 $ 451.5 Gross profit $ 34.3 $ 41.2 $ 69.7 $ 79.6 Net earnings (loss) $ 0.3 $ (7.2) $ (1.1) $ (8.1) Less: Preferred stock dividend 8.8 8.0 17.6 15.8 Net Loss Available to 8th Avenue Common Shareholders $ (8.5) $ (15.2) $ (18.7) $ (23.9) The Company provides services to 8th Avenue under a master services agreement (the “MSA”), as well as certain advisory services for a fee. The Company recorded MSA and advisory income of $0.8 and $1.6 during the three and six months ended March 31, 2021, respectively, and $1.0 and $2.0 during the three and six months ended March 31, 2020, respectively, which were recorded in “Selling, general and administrative expenses” in the Condensed Consolidated Statements of Operations. During the three and six months ended March 31, 2021, the Company had net sales to 8th Avenue of $2.0 and $4.0, respectively, and purchases from and royalties paid to 8th Avenue of $15.4 and $17.6, respectively. During the three and six months ended March 31, 2020, the Company had net sales to 8th Avenue of $1.6 and $3.2, respectively, and purchases from and royalties paid to 8th Avenue of $2.4 and $5.2, respectively. Sales and purchases between the Company and 8th Avenue were all made at arm’s-length. The investment in 8th Avenue was $95.4 and $110.1 at March 31, 2021 and September 30, 2020, respectively, and was included in “Equity method investments” on the Condensed Consolidated Balance Sheets. The Company had current receivables, current payables and a long-term liability with 8th Avenue of $4.7, $5.5 and $0.7, respectively, at March 31, 2021 and current receivables, current payables and a long-term liability of $3.2, $0.6 and $0.7, respectively, at September 30, 2020. The current receivables, current payables and long-term liability, which related to the separation of 8th Avenue from the Company, MSA fees, pass through charges owed by 8th Avenue to the Company and related party sales and purchases, were included in “Receivables, net,” “Accounts payable” and “Other liabilities,” respectively, on the Condensed Consolidated Balance Sheets. Alpen and Weetabix East Africa The Company holds an equity interest in two legal entities, Alpen Food Company South Africa (Pty) Limited (“Alpen”) and Weetabix East Africa Limited (“Weetabix East Africa”). Alpen is a South African-based company that produces ready-to-eat (“RTE”) cereal and muesli. The Company owns 50% of Alpen’s common stock with no other indicators of control, and accordingly, the Company accounts for its investment in Alpen using the equity method. The Company’s equity method loss, net of tax, attributable to Alpen was $(0.2) for both the three and six months ended March 31, 2021 and $(0.2) and $(0.5) for the three and six months ended March 31, 2020, respectively, and was included in “Equity method loss, net of tax” in the Condensed Consolidated Statements of Operations. The investment in Alpen was $4.3 and $4.0 at March 31, 2021 and September 30, 2020, respectively, and was included in “Equity method investments” on the Condensed Consolidated Balance Sheets. The Company had a note receivable balance with Alpen of $0.5 at both March 31, 2021 and September 30, 2020, which was included in “Other assets” on the Condensed Consolidated Balance Sheets.

Business Combinations

Business Combinations	6 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Business Combinations	BUSINESS COMBINATIONS The Company accounts for acquisitions using the acquisition method of accounting, whereby the results of operations are included in the financial statements from the date of acquisition. The purchase price is allocated to acquired assets and assumed liabilities based on their estimated fair values at the date of acquisition. Any excess of the purchase price over the estimated fair values of the identifiable net assets acquired is recorded as goodwill. Any excess of the estimated fair values of the identifiable net assets over the purchase price is recorded as a gain on bargain purchase. Goodwill represents the value the Company expects to achieve through the implementation of operational synergies and the expansion of the business into new or growing segments of the industry. Fiscal 2021 On January 25, 2021, the Company completed its acquisition of the Peter Pan nut butter brand (“Peter Pan”) from Conagra Brands, Inc. for $102.0, subject to working capital and other adjustments, resulting in a payment at closing of $103.4. The acquisition was completed using cash on hand. Peter Pan is a nationally recognized brand with a diversified customer base across key channels and is reported in the Post Consumer Brands segment (see Note 19). All Peter Pan nut butter products are currently co-manufactured by 8th Avenue, in which the Company has a 60.5% common equity interest (see Note 3). At March 31, 2021, the Company had recorded an estimated working capital receivable of $2.0, which was included in “Receivables, net” on the Condensed Consolidated Balance Sheet. Based upon the preliminary purchase price allocation, the Company has recorded customer relationships and trademarks and brands of $12.0 and $55.0, respectively, both of which will be amortized over a weighted-average period of 20 years. Net sales and operating profit included in the Condensed Consolidated Statements of Operations attributable to Peter Pan was $17.4 and $3.5, respectively, for the three and six months ended March 31, 2021. On February 1, 2021, the Company completed its acquisition of the Almark Foods business and related assets (“Almark”) for $52.0, subject to working capital and other adjustments, resulting in a payment at closing of $51.3. The acquisition was completed using cash on hand. Almark is a provider of hard-cooked and deviled egg products, offering conventional, organic and cage-free products, and distributes its products to foodservice distributors. Almark is reported in the Foodservice segment (see Note 19). Based upon the preliminary purchase price allocation, the Company has recorded $19.5 of customer relationships to be amortized over a weighted-average period of 10 years. Net sales and operating profit included in the Condensed Consolidated Statements of Operations attributable to Almark was $14.4 and $0.1, respectively, for the three and six months ended March 31, 2021. Preliminary values of the Peter Pan and Almark acquisitions are not yet finalized pending the final purchase price allocations and are subject to change once additional information is obtained. The Company expects a portion of the final fair value of goodwill related to the acquisition of Peter Pan and the final fair value of goodwill related to the acquisition of Almark to be deductible for U.S. income tax purposes. The following table provides the preliminary purchase price allocation related to the fiscal 2021 acquisitions of Peter Pan and Almark based upon the fair values of assets and liabilities assumed, including the provisional amounts recognized related to the acquisitions, as of March 31, 2021. Peter Pan Almark Receivables $ — $ 6.4 Inventories 4.6 5.2 Prepaid expenses and other current assets — 0.1 Property — 9.8 Goodwill 55.1 19.7 Other intangible assets 67.0 19.5 Deferred tax asset — 1.3 Other assets — 32.9 Accounts payable (11.7) (5.4) Other current liabilities — (1.6) Deferred tax liability (13.6) — Other liabilities — (36.6) Total acquisition cost $ 101.4 $ 51.3 Fiscal 2020 On July 1, 2020, the Company completed its acquisition of Henningsen Foods, Inc. (“Henningsen”) from a subsidiary of Kewpie Corporation for $20.0, subject to working capital and other adjustments, resulting in a payment at closing of $22.7. The acquisition was completed using cash on hand. Henningsen is a producer of egg and meat products and is reported in the Foodservice segment (see Note 19). Based upon the preliminary purchase price allocation at September 30, 2020, the Company identified and recorded $32.6 of net assets, including cash of $2.8, which exceeded the purchase price paid for Henningsen. As a result, the Company recorded a gain of $11.7, which was reported as other operating income in the consolidated statement of operations for the year ended September 30, 2020. At September 30, 2020, the Company had recorded an estimated working capital settlement receivable of $1.8, which was included in “Receivables, net” on the Condensed Consolidated Balance Sheet. In the three months ended March 31, 2021, the Company recorded measurement period adjustments related to inventory and deferred income taxes and, as a result, recorded a gain of $2.2, which was included in “Other operating (income) expenses, net” in the Condensed Consolidated Statement of Operations for the three months ended March 31, 2021. In the six months ended March 31, 2021, the Company recorded measurement period adjustments related to inventory and deferred income taxes of $0.7 and reached a final settlement of net working capital, resulting in an amount received by the Company of $1.0. As a result of these adjustments, the Company recorded a loss of $0.1, which was included in “Other operating (income) expenses, net” in the Condensed Consolidated Statement of Operations for the six months ended March 31, 2021. Unaudited Pro Forma Information The following unaudited pro forma information presents a summary of the results of operations of the Company combined with the results of Peter Pan and Almark for the periods presented as if the fiscal 2021 acquisitions had occurred on October 1, 2019, along with certain pro forma adjustments. These pro forma adjustments give effect to the amortization of certain definite-lived intangible assets, adjusted depreciation based upon fair value of assets acquired, interest expense, transaction costs and related income taxes. The following unaudited pro forma information has been prepared for comparative purposes only and is not necessarily indicative of the results of operations as they would have been had the acquisitions occurred on the assumed dates, nor is it necessarily an indication of future operating results. Three Months Ended Six Months Ended 2021 2020 2021 2020 Pro forma net sales $ 1,494.3 $ 1,549.9 $ 2,985.9 $ 3,060.4 Pro forma net earnings (loss) available to common shareholders $ 110.5 $ (188.0) $ 191.9 $ (94.1) Pro forma basic earnings (loss) per common share $ 1.72 $ (2.71) $ 2.96 $ (1.34) Pro forma diluted earnings (loss) per common share $ 1.70 $ (2.71) $ 2.91 $ (1.34)

Restructuring (Notes)

Restructuring (Notes)	6 Months Ended
	Mar. 31, 2021
Restructuring [Abstract]
Restructuring	RESTRUCTURING In October 2020, BellRing announced its plan to strategically realign its business, resulting in the closing of its Dallas, Texas office and the downsizing of its Munich, Germany location (the “BellRing Restructuring”). The BellRing Restructuring is expected to be completed by June 30, 2021. Restructuring charges and the associated liabilities for employee-related costs are shown in the following table. Balance, September 30, 2020 $ — Charge to expense 4.8 Cash payments (3.7) Non-cash charges — Balance, March 31, 2021 $ 1.1 Total expected restructuring charges $ 4.9 Cumulative restructuring charges incurred to date 4.8 Remaining expected restructuring charges $ 0.1 During the three and six months ended March 31, 2021, the Company incurred total restructuring charges of $0.3 and $4.8, respectively, related to the BellRing Restructuring. No restructuring charges were incurred during the three or six months ended March 31, 2020. Restructuring charges were included in “Selling, general and administrative expenses” in the Condensed Consolidated Statements of Operations. These expenses are included in the measure of segment performance for BellRing Brands (see Note 19).

Amounts Held for Sale (Notes)

Amounts Held for Sale (Notes)	6 Months Ended
	Mar. 31, 2021
Assets and Liabilities Held for Sale [Abstract]
Amounts Held for Sale	AMOUNTS HELD FOR SALE At September 30, 2020, the Company had a Post Consumer Brands RTE cereal manufacturing plant in Clinton, Massachusetts (the “Clinton Plant”) with a book value of $3.4 classified as held for sale, land and a building at its Post Consumer Brands RTE cereal manufacturing facility in Asheboro, North Carolina (the “Asheboro Facility”) with a combined book value of $1.4 classified as held for sale and land and a building at one of its Weetabix manufacturing facilities in Corby, United Kingdom (the “Corby Facility”) with a combined book value of $2.5 classified as held for sale. These assets held for sale were reported as “Prepaid expenses and other current assets” on the Condensed Consolidated Balance Sheet. The Company sold a portion of the Clinton Plant, the Asheboro Facility and the Corby Facility in November 2020 and the remaining portion of the Clinton Plant in February 2021.In the three months ended March 31, 2021, a loss on assets held for sale of $0.1 was recorded related to the sale of the remaining portion of the Clinton Plant sold in February 2021. In the six months ended March 31, 2021, a net gain on assets held for sale of $0.5 was recorded consisting of (i) a gain of $0.7 related to the sale of the Corby Facility in November 2020, (ii) a loss of $0.1 related to the sale of the Asheboro Facility in November 2020 and (iii) a loss of $0.1 related to the sale of the remaining portion of the Clinton Plant in February 2021. These held for sale adjustments were included in “Other operating (income) expenses, net” in the Condensed Consolidated Statements of Operations for the three and six months ended March 31, 2021. There were no held for sale gains or losses recorded in the three or six months ended March 31, 2020.

Earnings (Loss) Per Share

Earnings (Loss) Per Share	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings (Loss) per Share	EARNINGS (LOSS) PER SHAREBasic earnings (loss) per share is based on the average number of common shares outstanding during the period. Diluted earnings (loss) per share is based on the average number of shares used for the basic earnings (loss) per share calculation, adjusted for the dilutive effect of stock options, stock appreciation rights and restricted stock units using the “treasury stock” method. In addition, “Net earnings (loss) for diluted earnings (loss) per share” in the table below has been adjusted for the Company’s share of BellRing’s consolidated net earnings (loss) for diluted earnings (loss) per share, to the extent it is dilutive. The following table sets forth the computation of basic and diluted earnings (loss) per share. Three Months Ended Six Months Ended 2021 2020 2021 2020 Net earnings (loss) for basic earnings (loss) per share $ 109.9 $ (191.4) $ 191.1 $ (92.2) Dilutive impact of BellRing net earnings — — — — Net earnings (loss) for diluted earnings (loss) per share $ 109.9 $ (191.4) $ 191.1 $ (92.2) Weighted-average shares for basic earnings (loss) per share 64.1 69.3 64.9 70.0 Effect of dilutive securities: Stock options 0.6 — 0.6 — Stock appreciation rights 0.1 — 0.1 — Restricted stock units 0.2 — 0.3 — Performance-based restricted stock units 0.1 — 0.1 — Total dilutive securities 1.0 — 1.1 — Weighted-average shares for diluted earnings (loss) per share 65.1 69.3 66.0 70.0 Basic earnings (loss) per common share $ 1.71 $ (2.76) $ 2.94 $ (1.32) Diluted earnings (loss) per common share $ 1.69 $ (2.76) $ 2.90 $ (1.32) The following table details the securities that have been excluded from the calculation of weighted-average shares for diluted earnings (loss) per share as they were anti-dilutive. Three Months Ended Six Months Ended 2021 2020 2021 2020 Stock options 0.1 1.7 0.1 1.7 Stock appreciation rights — 0.1 — 0.1 Restricted stock units — 1.0 — 1.0 Performance-based restricted stock units 0.1 0.2 0.1 0.2

Inventories

Inventories	6 Months Ended
	Mar. 31, 2021
Inventory [Abstract]
Inventories	INVENTORIES March 31, September 30, Raw materials and supplies $ 112.3 $ 118.1 Work in process 19.7 17.8 Finished products 471.7 429.4 Flocks 36.0 34.1 $ 639.7 $ 599.4

Property, net

Property, net	6 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, net	PROPERTY, NET March 31, September 30, Property, at cost $ 3,073.3 $ 2,979.2 Accumulated depreciation (1,296.7) (1,199.5) $ 1,776.6 $ 1,779.7

Goodwill (Notes)

Goodwill (Notes)	6 Months Ended
	Mar. 31, 2021
Goodwill [Abstract]
Goodwill	GOODWILL The changes in the carrying amount of goodwill by segment are noted in the following table. Post Consumer Brands Weetabix Foodservice Refrigerated Retail BellRing Brands Total Balance, September 30, 2020 Goodwill (gross) $ 2,011.8 $ 889.5 $ 1,335.6 $ 793.6 $ 180.7 $ 5,211.2 Accumulated impairment losses (609.1) — — (48.7) (114.8) (772.6) Goodwill (net) $ 1,402.7 $ 889.5 $ 1,335.6 $ 744.9 $ 65.9 $ 4,438.6 Goodwill acquired 55.1 — 19.7 — — 74.8 Currency translation adjustment 0.2 61.0 — — — 61.2 Balance, March 31, 2021 Goodwill (gross) $ 2,067.1 $ 950.5 $ 1,355.3 $ 793.6 $ 180.7 $ 5,347.2 Accumulated impairment losses (609.1) — — (48.7) (114.8) (772.6) Goodwill (net) $ 1,458.0 $ 950.5 $ 1,355.3 $ 744.9 $ 65.9 $ 4,574.6

Intangible Assets, net

Intangible Assets, net	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, net	INTANGIBLE ASSETS, NET Total intangible assets are as follows: March 31, 2021 September 30, 2020 Carrying Accumulated Net Carrying Accumulated Net Subject to amortization: Customer relationships $ 2,348.1 $ (754.8) $ 1,593.3 $ 2,304.8 $ (681.9) $ 1,622.9 Trademarks and brands 852.0 (295.6) 556.4 795.0 (266.9) 528.1 Other intangible assets 3.1 (3.1) — 3.1 (3.1) — 3,203.2 (1,053.5) 2,149.7 3,102.9 (951.9) 2,151.0 Not subject to amortization: Trademarks and brands 1,064.5 — 1,064.5 1,046.5 — 1,046.5 $ 4,267.7 $ (1,053.5) $ 3,214.2 $ 4,149.4 $ (951.9) $ 3,197.5 In December 2020, BellRing finalized its plan to discontinue the Supreme Protein brand and related sales of Supreme Protein products. In connection with the discontinuance, BellRing updated the useful lives of the customer relationships and trademarks associated with the Supreme Protein brand to reflect the remaining period in which BellRing expects to continue to sell existing Supreme Protein product inventory. Accelerated amortization of $17.7 and $18.1 was recorded during the three and six months ended March 31, 2021, respectively, resulting from the updated useful lives of the customer relationships and trademarks associated with the Supreme Protein brand. The net carrying values of the customer relationships and trademarks associated with the Supreme Protein brand were $7.5 and $4.7 as of March 31, 2021, respectively, which are expected to be fully amortized by June 1, 2021.

Derivative Financial Instrument

Derivative Financial Instruments and Hedging	6 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging	DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING In the ordinary course of business, the Company is exposed to commodity price risks relating to the purchases of raw materials and supplies, interest rate risks relating to variable rate debt and foreign currency exchange rate risks. The Company utilizes derivative financial instruments, including (but not limited to) futures contracts, option contracts, forward contracts and swaps, to manage certain of these exposures by hedging when it is practical to do so. The Company does not hold or issue financial instruments for speculative or trading purposes. At March 31, 2021, the Company’s derivative instruments, none of which were designated as hedging instruments under ASC Topic 815, “Derivatives and Hedging,” consisted of: • Commodity and energy futures, swaps and option contracts, which relate to inputs that generally will be utilized within the next two years; • foreign currency forward contracts maturing in the next year that have the effect of hedging currency fluctuations between the U.S. Dollar and the Pound Sterling; • interest rate swaps that have the effect of hedging interest payments on debt expected to be issued but not yet priced, including: ◦ pay-fixed, receive-variable interest rate swaps maturing in May 2021 and May 2024 that require monthly settlements; ◦ rate-lock interest rate swaps that require lump sum settlements with the first settlement occurring in July 2021 and th e last in July 2026; and ◦ interest rate swaps that mature in July 2021 and give the Company the option of pay-variable, receive-fixed lump sum settlements; and • pay-fixed, receive-variable interest rate swaps maturing in December 2022 that require monthly settlements and have the effect of hedging forecasted interest payments on BellRing’s variable rate debt. Interest rate swaps In the second quarter of fiscal 2021, the Company restructured two of its rate-lock interest rate swap contracts, both of which contain a non-cash, off-market financing element. There were no cash settlements paid or received in connection with these restructurings. In the first quarter of fiscal 2020, contemporaneously with the repayment of its term loan, the Company changed the designation of one of its interest rate swap contracts from a cash flow hedge to a non-designated hedging instrument. In connection with the de-designation, the Company reclassified losses previously recorded in accumulated other comprehensive income (loss) (“OCI”) of $7.2 to “Interest expense, net” in the Condensed Consolidated Statement of Operations for the six months ended March 31, 2020. As of April 1, 2020, the Company changed the designation of its interest rate swap contracts that are used as hedges of forecasted interest payments on BellRing’s variable rate debt from cash flow hedges to non-designated hedging instruments as the swaps were no longer effective (as defined by ASC Topic 815). In connection with the de-designation, the Company started reclassifying losses previously recorded in accumulated OCI to “Interest expense, net” in the Condensed Consolidated Statements of Operations on a straight-line basis over the term of BellRing’s variable rate debt. Mark-to-market adjustments related to these swaps will also be included in “Interest expense, net” in the Condensed Consolidated Statements of Operations. At March 31, 2021 and September 30, 2020, the remaining net loss before taxes to be amortized was $8.3 and $9.4, respectively. Cross-currency swaps The Company terminated $448.7 notional value of its cross-currency swap contracts that were designated as hedging instruments during the second quarter of fiscal 2020. In connection with this termination, the Company received cash proceeds of $50.3 during the three and six months ended March 31, 2020, which was recorded in accumulated OCI. Reclassification of amounts recorded in accumulated OCI into earnings will only occur in the event United Kingdom-based operations are substantially liquidated. The following table shows the notional amounts of derivative instruments held. March 31, September 30, Commodity contracts $ 36.7 $ 24.7 Energy contracts 65.9 87.1 Foreign exchange contracts - Forward contracts 20.9 28.9 Interest rate swaps 620.9 621.7 Interest rate swaps - Rate-lock swaps 1,609.8 1,666.0 Interest rate swaps - Options 433.3 433.3 The following table presents the balance sheet location and fair value of the Company’s derivative instruments. The Company does not offset derivative assets and liabilities within the Condensed Consolidated Balance Sheets. Balance Sheet Location March 31, September 30, Asset Derivatives: Commodity contracts Prepaid expenses and other current assets $ 8.2 $ 5.0 Energy contracts Prepaid expenses and other current assets 5.2 1.8 Commodity contracts Other assets 6.0 0.1 Energy contracts Other assets 4.1 0.9 Foreign exchange contracts Prepaid expenses and other current assets — 0.1 Interest rate swaps Prepaid expenses and other current assets — 6.8 Interest rate swaps Other assets 40.0 — $ 63.5 $ 14.7 Liability Derivatives: Commodity contracts Other current liabilities $ 0.6 $ 1.4 Energy contracts Other current liabilities — 10.1 Energy contracts Other liabilities — 3.9 Foreign exchange contracts Other current liabilities 1.1 — Interest rate swaps Other current liabilities 68.4 176.4 Interest rate swaps Other liabilities 247.8 351.3 $ 317.9 $ 543.1 The following tables present the effects of the Company’s derivative instruments on the Condensed Consolidated Statements of Operations and Condensed Consolidated Statements of Comprehensive Income (Loss) for the three months ended March 31, 2021 and 2020. Derivatives Not Designated as Hedging Instruments Statement of Operations Location (Gain) Loss Recognized in Statement of Operations 2021 2020 Commodity contracts Cost of goods sold $ (2.3) $ 8.0 Energy contracts Cost of goods sold (11.3) 26.0 Foreign exchange contracts Selling, general and administrative expenses (0.3) (0.1) Interest rate swaps Interest expense, net 0.5 — Interest rate swaps (Income) expense on swaps, net (185.6) 224.6 Derivatives Designated as Hedging Instruments Loss (Gain) Recognized in OCI including NCI Loss (Gain) Reclassified from Accumulated OCI including NCI into Earnings (a) Statement of Operations Location 2021 2020 2021 2020 Interest rate swaps $ — $ 11.0 $ 0.6 $ (0.2) Interest expense, net Cross-currency swaps — (66.8) — — (Income) expense on swaps, net (a) For the three months ended March 31, 2021, this amount includes the amortization of previously unrealized losses on BellRing’s interest rate swaps that were de-designated as hedging instruments as of April 1, 2020. The following table presents the components of the Company’s net hedging (gains) losses on interest rate swaps, which are included in “Interest expense, net” and “(Income) expense on swaps, net” in the Condensed Consolidated Statements of Operations, as well as cash settlements paid (received) during the periods presented. Three Months Ended Statement of Operations Location Mark-to-Market (Gain) Loss, net Net Loss Reclassified from Accumulated OCI including NCI (a) Total Net Hedging (Gain) Loss Cash Settlements Paid (Received), Net Interest expense, net $ (0.1) $ 0.6 $ 0.5 $ 1.2 (Income) expense on swaps, net (185.6) — (185.6) 13.6 2021 Total $ (185.7) $ 0.6 $ (185.1) $ 14.8 Interest expense, net $ (0.2) $ — $ (0.2) $ (0.2) (Income) expense on swaps, net 224.6 — 224.6 0.4 2020 Total $ 224.4 $ — $ 224.4 $ 0.2 (a) Includes the amortization of previously unrealized losses on BellRing’s interest rate swaps over the term of the related debt that were de-designated as hedging instruments, as well as the reclassification of previously unrealized losses on interest rate swaps that were de-designated as hedging instruments. The following tables present the effects of the Company’s derivative instruments on the Condensed Consolidated Statements of Operations and Condensed Consolidated Statements of Comprehensive Income (Loss) for the six months ended March 31, 2021 and 2020. Derivatives Not Designated as Hedging Instruments Statement of Operations Location (Gain) Loss Recognized in Statement of Operations 2021 2020 Commodity contracts Cost of goods sold $ (9.7) $ 6.1 Energy contracts Cost of goods sold (19.3) 23.5 Foreign exchange contracts Selling, general and administrative expenses 1.2 (0.1) Interest rate swaps Interest expense, net 1.0 — Interest rate swaps (Income) expense on swaps, net (227.2) 163.2 Derivatives Designated as Hedging Instruments Loss (Gain) Recognized in OCI including NCI Loss Reclassified from Accumulated OCI including NCI into Earnings (a) Statement of Operations Location 2021 2020 2021 2020 Interest rate swaps $ — $ 9.7 1.1 7.0 Interest expense, net Cross-currency swaps — (32.2) — — (Income) expense on swaps, net (a) For the six months ended March 31, 2021, this amount includes the amortization of previously unrealized losses on BellRing’s interest rate swaps that were de-designated as hedging instruments as of April 1, 2020. For the six months ended March 31, 2020, this amount includes the amortization of previously unrealized losses on interest rate swaps that were de-designated as hedging instruments in the first quarter of fiscal 2020. The following table presents the components of the Company’s net hedging (gains) losses on interest rate swaps, which are included in “Interest expense, net” and “(Income) expense on swaps, net” in the Condensed Consolidated Statements of Operations, as well as cash settlements paid (received) during the periods presented. Six Months Ended Statement of Operations Location Mark-to-Market (Gain) Loss, net Net Loss Reclassified from Accumulated OCI including NCI (a) Total Net Hedging (Gain) Loss Cash Settlements Paid (Received), Net Interest expense, net $ (0.1) $ 1.1 $ 1.0 $ 2.4 (Income) expense on swaps, net (227.2) — (227.2) 15.1 2021 Total $ (227.3) $ 1.1 $ (226.2) $ 17.5 Interest expense, net $ (0.2) $ 7.2 $ 7.0 $ (0.2) (Income) expense on swaps, net 163.2 — 163.2 19.5 2020 Total $ 163.0 $ 7.2 $ 170.2 $ 19.3 (a) Includes the amortization of previously unrealized losses on BellRing’s interest rate swaps over the term of the related debt that were de-designated as hedging instruments, as well as the reclassification of previously unrealized losses on interest rate swaps that were de-designated as hedging instruments. Accumulated OCI, including amounts reported as NCI, included a $91.3 net gain on hedging instruments before taxes ($68.8 after taxes) at March 31, 2021, compared to a $90.2 net gain before taxes ($67.9 after taxes) at September 30, 2020. Approximately $2.3 of the net hedging losses reported in accumulated OCI at March 31, 2021 are expected to be reclassified into earnings within the next 12 months. Accumulated OCI included settlements of and previously unrealized gains on cross-currency swaps of $99.5 at both March 31, 2021 and September 30, 2020. In connection with the settlements of cross-currency swaps, the Company recognized gains in accumulated OCI of $61.6 and $63.0 during the three and six months ended March 31, 2020, respectively. Reclassification of amounts recorded in accumulated OCI into earnings will only occur in the event United Kingdom-based operations are substantially liquidated.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The following table represents the Company’s assets and liabilities measured at fair value on a recurring basis and the basis for that measurement according to the levels in the fair value hierarchy in ASC Topic 820, “Fair Value Measurement.” March 31, 2021 September 30, 2020 Total Level 1 Level 2 Total Level 1 Level 2 Assets: Deferred compensation investments $ 14.8 $ 14.8 $ — $ 12.8 $ 12.8 $ — Derivative assets 63.5 — 63.5 14.7 — 14.7 Equity securities 46.7 46.7 — 27.9 27.9 — $ 125.0 $ 61.5 $ 63.5 $ 55.4 $ 40.7 $ 14.7 Liabilities: Deferred compensation liabilities $ 34.0 $ — $ 34.0 $ 29.7 $ — $ 29.7 Derivative liabilities 317.9 — 317.9 543.1 — 543.1 $ 351.9 $ — $ 351.9 $ 572.8 $ — $ 572.8 The deferred compensation investments are primarily invested in mutual funds, and the fair value is measured using the market approach. These investments are in the same funds, or funds that employ a similar investment strategy, and are purchased in substantially the same amounts, as the participants’ selected investment options (excluding Post common stock equivalents), which represent the underlying liabilities to participants in the Company’s deferred compensation plans. Deferred compensation liabilities are recorded at amounts due to participants in cash, based on the fair value of participants’ selected investment options (excluding certain Post common stock equivalents to be distributed in shares) using the market approach. The Company utilizes the income approach to measure fair value for its commodity and energy derivatives. The income approach uses pricing models that rely on market observable inputs such as yield curves and forward prices. Foreign exchange contracts are valued using the spot rate less the forward rate multiplied by the notional amount. The Company’s calculation of the fair value of interest rate swaps is derived from a discounted cash flow analysis based on the terms of the contract and the interest rate curve. Refer to Note 12 for the classification of changes in fair value of derivative assets and liabilities measured at fair value on a recurring basis within the Condensed Consolidated Statements of Operations. The Company uses the market approach to measure the fair value of its equity securities. The Company’s financial assets and liabilities also include cash and cash equivalents, receivables and accounts payable for which the carrying value approximates fair value due to their short maturities (less than 12 months). The Company does not record its current portion of long-term debt and long-term debt at fair value on the Condensed Consolidated Balance Sheets. The fair values of any outstanding borrowings under the municipal bond and the BellRing Revolving Credit Facility (as defined in Note 16) as of March 31, 2021 and September 30, 2020 approximated their carrying values. Based on current market rates, the fair value of the Company’s debt, excluding any outstanding borrowings under the municipal bond and the BellRing Revolving Credit Facility (both of which are categorized as Level 2), was $7,216.5 and $7,277.8 as of March 31, 2021 and September 30, 2020, respectively. Certain assets and liabilities, including property, plant and equipment, goodwill and other intangible assets and assets held for sale, are measured at fair value on a non-recurring basis. At September 30, 2020, the Company had land and buildings classified as assets held for sale related to the closures of the Company’s Clinton Plant, Asheboro Facility and Corby Facility. The Company sold the Asheboro Facility, the Corby Facility and a portion of the Clinton Plant in November 2020 and the remaining portion of the Clinton Plant in February 2021. The Clinton Plant and Asheboro Facility were both reported in the Post Consumer Brands segment, and the Corby Facility was reported in the Weetabix segment. For additional information on assets held for sale, see Note 6. The fair value of assets held for sale was measured on a non-recurring basis based on the lower of book value or third party valuations. When applicable, the fair value is adjusted to reflect an offer to purchase the assets. The fair value measurement was categorized as Level 3, as the fair values utilize significant unobservable inputs. The following table summarizes the Level 3 activity. Balance, September 30, 2020 $ 7.3 Net gain related to assets held for sale 0.5 Proceeds from the sale of assets held for sale (7.9) Currency translation adjustment 0.1 Balance, March 31, 2021 $ —

Commitments and Contingencies (

Commitments and Contingencies (Notes)	6 Months Ended
	Mar. 31, 2021
Legal Proceedings [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Legal Proceedings Antitrust Claims In late 2008 and early 2009, approximately 22 class action lawsuits were filed in various federal courts against Michael Foods, Inc. (“MFI”), a wholly-owned subsidiary of the Company, and approximately 20 other defendants (producers of shell eggs and egg products and egg industry organizations), alleging violations of federal and state antitrust laws in connection with the production and sale of shell eggs and egg products, and seeking unspecified damages. All cases were transferred to the Eastern District of Pennsylvania for coordinated and/or consolidated pretrial proceedings. The cases involved three plaintiff groups: (i) a nationwide class of direct purchasers of shell eggs (the “direct purchaser class”); (ii) individual companies (primarily large grocery chains and food companies that purchase considerable quantities of eggs) that opted out of various settlements and filed their own complaints related to their purchases of shell eggs and egg products (“opt-out plaintiffs”); and (iii) indirect purchasers of shell eggs (“indirect purchaser plaintiffs”). Resolution of claims: To date, MFI has resolved the following claims, including all class claims: (i) in December 2016, MFI settled all claims asserted against it by the direct purchaser class for a payment of $75.0, which was approved by the district court in December 2017; (ii) in January 2017, MFI settled all claims asserted against it by opt-out plaintiffs related to shell egg purchases on confidential terms; (iii) in June 2018, MFI settled all claims asserted against it by indirect purchaser plaintiffs on confidential terms; and (iv) between June 2019 and September 2019, MFI individually settled on confidential terms egg product opt-out claims asserted against it by four separate opt-out plaintiffs. MFI has at all times denied liability in this matter, and no settlement contains any admission of liability by MFI. Remaining portion of the cases: MFI remains a defendant only with respect to claims that seek damages based on purchases of egg products by three opt-out plaintiffs. The district court had granted summary judgment precluding any claims for egg products purchases by such opt-out plaintiffs, but the Third Circuit Court of Appeals reversed and remanded these claims for further pre-trial proceedings. Defendants filed a second motion for summary judgment seeking dismissal of the claims, which was denied in June 2019. The remaining opt-out plaintiffs have not yet been assigned trial dates. Although the likelihood of a material adverse outcome in the egg antitrust litigation has been significantly reduced as a result of the MFI settlements described above, the remaining portion of the cases could still result in a material adverse outcome. No expense was recorded in the Condensed Consolidated Statements of Operations related to these matters for the three or six months ended March 31, 2021 or 2020. At both March 31, 2021 and September 30, 2020, the Company had $3.5 accrued for this matter, which was included in “Other current liabilities” on the Condensed Consolidated Balance Sheets. The Company records reserves for litigation losses in accordance with ASC Topic 450, “Contingencies.” Under ASC Topic 450, a loss contingency is recorded if a loss is probable and can be reasonably estimated. The Company records probable loss contingencies based on the best estimate of the loss. If a range of loss can be reasonably estimated, but no single amount within the range appears to be a better estimate than any other amount within the range, the minimum amount in the range is accrued. These estimates are often initially developed earlier than when the ultimate loss is known, and the estimates are adjusted if additional information becomes known. Although the Company believes its accruals for this matter are appropriate, the final amounts required to resolve such matter could differ materially from recorded estimates and the Company’s consolidated financial condition, results of operations and cash flows could be materially affected. Under current law, any settlement paid, including the settlements with the direct purchaser plaintiffs, the opt-out plaintiffs and the indirect purchaser plaintiffs, is deductible for federal income tax purposes. Other The Company is subject to various other legal proceedings and actions arising in the normal course of business. In the opinion of management, based upon the information presently known, the ultimate liability, if any, arising from such pending legal proceedings, as well as from asserted legal claims and known potential legal claims which are likely to be asserted, taking into account established accruals for estimated liabilities (if any), are not expected to be material individually or in the aggregate to the consolidated financial condition, results of operations or cash flows of the Company. In addition, although it is difficult to estimate the potential financial impact of actions regarding expenditures for compliance with regulatory matters, in the opinion of management, based upon the information currently available, the ultimate liability arising from such compliance matters is not expected to be material to the consolidated financial condition, results of operations or cash flows of the Company.

Leases (Notes)

Leases (Notes)	6 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	LEASES The Company leases office space, certain warehouses and equipment primarily through operating lease agreements. The Company has no material finance lease agreements. Leases have remaining terms which range from less than 1 year to 56 years and most leases provide the Company with the option to exercise one or more renewal terms. The weighted average remaining lease term of the Company’s operating leases was approximately 9 years and 7 years as of March 31, 2021 and September 30, 2020, respectively, and the weighted average incremental borrowing rate was 4.63% and 4.40% at March 31, 2021 and September 30, 2020, respectively. Right-of-use (“ROU”) assets are recorded as “Other assets” and lease liabilities are recorded as “Other current liabilities” and “Other liabilities” on the Condensed Consolidated Balance Sheets. Operating lease expense is recognized on a straight-line basis over the lease term and is included in either “Cost of goods sold” or “Selling, general and administrative expenses” in the Condensed Consolidated Statements of Operations. Costs associated with finance leases and lease income do not have a material impact on the Company’s financial statements. The following table presents the balance sheet location of the Company’s operating leases. March 31, September 30, ROU assets: Other assets $ 141.1 $ 116.3 Lease liabilities: Other current liabilities $ 25.8 $ 23.6 Other liabilities 130.2 103.0 Total lease liabilities $ 156.0 $ 126.6 The following table presents maturities of the Company’s operating lease liabilities. March 31, Remaining Fiscal 2021 $ 16.0 Fiscal 2022 31.3 Fiscal 2023 27.8 Fiscal 2024 21.0 Fiscal 2025 14.9 Thereafter 79.6 Total future minimum payments $ 190.6 Less: Implied interest 34.6 Total lease liabilities $ 156.0 The following table presents supplemental operations statement information related to the Company’s operating leases. Three Months Ended Six Months Ended 2021 2020 2021 2020 Operating lease expense $ 11.0 $ 10.1 $ 21.4 $ 21.1 Variable lease expense 1.2 1.3 2.7 2.5 Short-term lease expense 2.0 1.7 3.6 3.7

Long-Term Debt

Long-Term Debt	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Long-Term Debt	LONG-TERM DEBT Long-term debt as of the dates indicated consisted of the following: March 31, September 30, 4.50% Senior Notes maturing September 2031 $ 1,800.0 $ — 4.625% Senior Notes maturing April 2030 1,650.0 1,650.0 5.50% Senior Notes maturing December 2029 750.0 750.0 5.625% Senior Notes maturing January 2028 940.9 940.9 5.75% Senior Notes maturing March 2027 1,299.3 1,299.3 5.00% Senior Notes maturing August 2026 — 1,697.3 BellRing Term B Facility 627.4 673.7 BellRing Revolving Credit Facility — 30.0 Municipal bond 7.5 8.5 $ 7,075.1 $ 7,049.7 Less: Current portion of long-term debt 74.3 64.9 Debt issuance costs, net 55.7 62.6 Plus: Unamortized premium and discount, net 35.9 36.8 Total long-term debt $ 6,981.0 $ 6,959.0 Senior Notes On March 10, 2021, th e Company issued $1,800.0 principal value of 4.50% senior notes maturing i n September 2 031. The 4.50% senior n otes were issued at par, and the Company receive d $1,783.2 after incurring investment banking and other fees and expenses of $16.8, which will be d eferred and amortized to interest expense over the term of the notes. Interest payments will be du e semi-annually each March 15 and September 15, beginning on September 15, 2021. With the net proceeds received from the issuance, the Company redeemed the outstanding principal balance of the 5.00% senior notes. For additional information, see “Repayments of Long-Term Debt” below. Credit Agreement On March 18, 2020, the Company entered into a second amended and restated credit agreement (the “Credit Agreement”). The Credit Agreement provides for a revolving credit facility in an aggregate principal amount of $750.0 (the “Revolving Credit Facility”), with the commitments thereunder to be made available to the Company in U.S. Dollars, Canadian Dollars, Euros or Pounds Sterling. Letters of credit are available under the Credit Agreement in an aggregate amount of up to $75.0 . The Revolving Credit Facility has outstanding letters of cre dit of $19.3, which reduced the available borrowing capacity under the Revolving Credit Facility to $730.7 at March 31, 2021. Any outstanding amounts under the Revolving Credit Facility must be repaid on or before March 18, 2025. The Credit Agreement provides for potential incremental revolving and term facilities at the request of the Company and at the discretion of the lenders or other persons providing such incremental facilities, in each case on terms to be determined, and also permits the Company to incur other secured or unsecured debt, in all cases subject to conditions and limitations on the amount as specified in the Credit Agreement. The Credit Agreement permits the Company to designate certain of its subsidiaries as unrestricted subsidiaries and once so designated, permits the disposition of (and authorizes the release of liens on) the assets of, and the equity interests in, such unrestricted subsidiaries and permits the release of such unrestricted subsidiaries as guarantors under the Credit Agreement. The Company’s obligations under the Credit Agreement are unconditionally guaranteed by its existing and subsequently acquired or organized domestic subsidiaries (other than immaterial subsidiaries, certain excluded subsidiaries and subsidiaries the Company designates as unrestricted subsidiaries, which include 8th Avenue and its subsidiaries and BellRing Brands, Inc. and its subsidiaries) and are secured by security interests in substantially all of the Company’s assets and the assets of its subsidiary guarantors, but excluding, in each case, real property. Borrowings under the Revolving Credit Facility bear interest, at the option of the Company, at an annual rate equal to either (a) the Eurodollar rate or (b) the base rate determined by reference to the highest of (i) the prime rate, (ii) the federal funds rate plus 0.50% per annum and (iii) the one-month Eurodollar rate plus 1.00% per annum, in each case plus an applicable margin, which initially were 1.50% for Eurodollar rate-based loans and 0.50% for base rate-based loans, and thereafter, will be determined by reference to the secured net leverage ratio (as defined in the Credit Agreement), with the applicable margin for Eurodollar rate loans and base rate loans being (i) 2.00% and 1.00%, respectively, if the secured net leverage ratio is greater than or equal to 3.00:1.00, (ii) 1.75% and 0.75%, respectively, if the secured net leverage ratio is less than 3.00:1.00 and greater than or equal to 1.50:1.00 or (iii) 1.50% and 0.50%, respectively, if the secured net leverage ratio is less than 1.50:1.00. Commitment fees on the daily unused amount of commitments under the Revolving Credit Facility initially accrued at the rate of 0.25%, and thereafter, will accrue at a rate of 0.375% if the Company’s secured net leverage ratio is greater than 3.00:1.00, and will accrue at a rate of 0.25% if the Company’s secured net leverage ratio is less than or equal to 3.00:1.00. The Credit Agreement provides for customary events of default, including material breach of representations and warranties, failure to make required payments, failure to comply with certain agreements or covenants, failure to pay or default under certain other indebtedness in excess of $100.0, certain events of bankruptcy and insolvency, inability to pay debts, the occurrence of one or more unstayed or undischarged judgments in excess of $100.0, attachments issued against all or any material part of the Company’s property, certain events under the Employee Retirement Income Security Act of 1974 (“ERISA”), a change of control (as defined in the Credit Agreement), the invalidity of any loan document and the failure of the collateral documents to create a valid and perfected first priority lien (subject to certain permitted liens). Upon the occurrence and during the continuance of an event of default, the maturity of the loans under the Credit Agreement may accelerate and the agent and lenders under the Credit Agreement may exercise other rights and remedies available at law or under the loan documents, including with respect to the collateral and guarantees of the Company’s obligations under the Credit Agreement. Municipal Bond In connection with the ongoing construction of a filtration system at the Company’s potato plant in Chaska, Minnesota, the Company continues to incur debt that guarantees the repayment of certain industrial revenue bonds used to finance the construction of the project. Principal payments are due annually on March 1, and interest payments are due semi-annually each March 1 and September 1. The debt matures on March 1, 2028. BellRing’s Credit Agreement and Senior Debt Facilities On October 21, 2019, BellRing entered into a credit agreement (as subsequently amended, the “BellRing Credit Agreement”), which provides for a term B loan facility in an aggregate principal amount of $700.0 (the “BellRing Term B Facility”) and a revolving credit facility in an aggregate principal amount of $200.0 (the “BellRing Revolving Credit Facility”), with the commitments under the BellRing Revolving Credit Facility to be made available to BellRing in U.S. Dollars, Euros or Pounds Sterling. Letters of credit are available under the BellRing Credit Agreement in an aggregate amount of up to $20.0. Any outstanding amounts under the BellRing Revolving Credit Facility and BellRing Term B Facility must be repaid on or before October 21, 2024. On February 26, 2021, BellRing entered into a second amendment to the BellRing Credit Agreement (the “BellRing Amendment”). The BellRing Amendment provided for the refinancing of the BellRing Term B Facility on substantially the same terms as in effect prior to the BellRing Amendment, except that it (i) reduced the interest rate margin by 100 basis points, resulting in (A) for Eurodollar rate loans, an interest rate of the Eurodollar rate plus a margin of 4.00% and (B) for base rate loans, an interest rate of the base rate plus a margin of 3.00%, (ii) reduced the floor for the Eurodollar rate to 0.75%, (iii) modified the BellRing Credit Agreement to address the anticipated unavailability of LIBOR as a reference interest rate and (iv) provided that if on or before August 26, 2021 BellRing repays the BellRing Term B Facility in whole or in part with the proceeds of new or replacement debt at a lower effective interest rate, or further amends the BellRing Credit Agreement to reduce the effective interest rate applicable to the BellRing Term B Facility, BellRing must pay a 1.00% premium on the amount repaid or subject to the interest rate reduction. In connection with the BellRing Amendment, BellRing paid debt refinancing fees of $1.5 in the three and six months ended March 31, 2021, which were included in “Loss on extinguishment and refinancing of debt, net” in the Condensed Consolidated Statements of Operations. Subsequent to the BellRing Amendment, borrowings under the BellRing Term B Facility bear interest, at the option of BellRing, at an annual rate equal to either (a) the Eurodollar rate or (b) the base rate determined by reference to the greatest of (i) the prime rate, (ii) the federal funds effective rate plus 0.50% per annum and (iii) the one-month Eurodollar rate plus 1.00% per annum, in each case plus an applicable margin of 4.00% for Eurodollar rate-based loans and 3.00% for base rate-based loans. The BellRing Term B Facility requires quarterly scheduled amortization payments of $8.75, which began on March 31, 2020, with the balance to be paid at maturity on October 21, 2024. Interest was paid on each Interest Payment Date (as defined in the BellRing Credit Agreement) during each of the six months ended March 31, 2021 and 2020. The BellRing Term B Facility contains customary mandatory prepayment provisions, including provisions for mandatory prepayment (a) from the net cash proceeds of certain asset sales and (b) of 75% of consolidated excess cash flow (as defined in the BellRing Credit Agreement) (which percentage will be reduced to 50% if the secured net leverage ratio (as defined in the BellRing Credit Agreement) is less than or equal to 3.35:1.00 as of a fiscal year end). During the six months ended March 31, 2021, BellRing repaid $28.8 on the BellRing Term B Facility as a mandatory prepayment from fiscal 2020 excess cash flow, which was in addition to the scheduled amortization payments. The Company classified $38.2 related to the estimated mandatory prepayment of fiscal 2021 excess cash flow in “Current portion of long-term debt” on the Condensed Consolidated Balance Sheet at March 31, 2021. BellRing may prepay the BellRing Term B Facility at its option without penalty or premium, except as provided in the BellRing Amendment. The interest rate on the BellRing Term B Facility was 4.75% and 6.00% as of March 31, 2021 and September 30, 2020, respectively. Borrowings under the BellRing Revolving Credit Facility bear interest, at the option of BellRing, at an annual rate equal to either the Eurodollar rate or the base rate (determined as described above) plus a margin, which initially was 4.25% for Eurodollar rate-based loans and 3.25% for base rate-based loans, and thereafter, will be determined by reference to the secured net leverage ratio, with the applicable margin for Eurodollar rate-based loans and base rate-based loans being (i) 4.25% and 3.25%, respectively, if the secured net leverage ratio is greater than or equal to 3.50:1.00, (ii) 4.00% and 3.00%, respectively, if the secured net leverage ratio is less than 3.50:1.00 and greater than or equal to 2.50:1.00 or (iii) 3.75% and 2.75%, respectively, if the secured net leverage ratio is less than 2.50:1.00. Facility fees on the daily unused amount of commitments under the BellRing Revolving Credit Facility initially accrued at the rate of 0.50% per annum and thereafter, depending on BellRing’s secured net leverage ratio, will accrue at rates ranging from 0.25% to 0.50% per annum. There were no amounts drawn under the BellRing Revolving Credit Facility as of March 31, 2021. The interest rate on the drawn portion of the BellRing Revolving Credit Facility was 5.25% as of September 30, 2020. During the six months ended March 31, 2021 and 2020, BellRing borrowed $20.0 and $185.0, respectively, under the BellRing Revolving Credit Facility and repaid $50.0 and $65.0, respectively, on the BellRing Revolving Credit Facility. The available borrowing capacity under the BellRing Revolving Credit Facility was $200.0 and $170.0 as of March 31, 2021 and September 30, 2020, respectively. There were no outstanding letters of credit as of March 31, 2021 or September 30, 2020. The BellRing Credit Agreement provides for incremental revolving and term facilities, and also permits other secured or unsecured debt, if, among other conditions, certain financial ratios are met, as defined and specified in the BellRing Credit Agreement. The BellRing Credit Agreement provides for customary events of default, including material breach of representations and warranties, failure to make required payments, failure to comply with certain agreements or covenants, failure to pay or default under certain other material indebtedness, certain events of bankruptcy and insolvency, inability to pay debts, the occurrence of one or more unstayed or undischarged judgments in excess of $65.0, certain events under ERISA, the invalidity of any loan document, a change in control and the failure of the collateral documents to create a valid and perfected first priority lien. Upon the occurrence and during the continuance of an event of default, the maturity of the loans under the BellRing Credit Agreement may accelerate and the agent and lenders under the BellRing Credit Agreement may exercise other rights and remedies available at law or under the loan documents, including with respect to the collateral and guarantees of BellRing’s obligations under the BellRing Credit Agreement. Obligations under the BellRing Credit Agreement are unconditionally guaranteed by the existing and subsequently acquired or organized domestic subsidiaries of BellRing (other than immaterial subsidiaries, certain excluded subsidiaries and subsidiaries of BellRing it designates as unrestricted subsidiaries) and are secured by security interests in substantially all of the assets of BellRing and the assets of its subsidiary guarantors (other than real property), subject to limited exceptions. The Company and its subsidiaries (other than BellRing and certain of its subsidiaries) are not obligors or guarantors under the BellRing debt facilities. Repayments of Long-Term Debt The following tables show the Company’s repayments of long-term debt and associated gain or loss included in “Loss on extinguishment and refinancing of debt, net” in the Condensed Consolidated Statements of Operations. Three Months Ended Repayments of Long-Term Debt Loss on Extinguishment and Refinancing of Debt, net Issuance or Borrowing Principal Amount Repaid Debt Premiums and Refinancing Fees Paid Write-off of Debt Issuance Costs and Deferred Financing Fees 5.00% Senior Notes $ 1,697.3 $ 74.3 $ 18.9 BellRing Revolving Credit Facility 50.0 — — BellRing Term B Facility 8.8 — — Municipal bond 1.0 — — BellRing Credit Agreement (a) — 1.5 — 2021 Total $ 1,757.1 $ 75.8 $ 18.9 5.50% Senior Notes maturing in March 2025 $ 1,000.0 $ 41.3 $ 8.7 8.00% Senior Notes 122.2 8.5 0.7 BellRing Revolving Credit Facility 25.0 — — BellRing Term B Facility 8.7 — — Municipal bond 1.1 — — Credit Agreement (b) — — 0.8 2020 Total $ 1,157.0 $ 49.8 $ 10.2 Six Months Ended Repayments of Long-Term Debt Loss on Extinguishment and Refinancing of Debt, net Issuance or Borrowing Principal Amount Repaid Debt Premiums and Refinancing Fees Paid Write-off of Debt Issuance Costs and Deferred Financing Fees 5.00% Senior Notes $ 1,697.3 $ 74.3 $ 18.9 BellRing Revolving Credit Facility 50.0 — — BellRing Term B Facility 46.3 — — Municipal bond 1.0 — — BellRing Credit Agreement (a) — 1.5 — 2021 Total $ 1,794.6 $ 75.8 $ 18.9 Term loan $ 1,309.5 $ — $ 9.1 Bridge loan 1,225.0 — 3.8 5.50% Senior Notes maturing in March 2025 1,000.0 41.3 8.7 8.00% Senior Notes 122.2 8.5 0.7 BellRing Revolving Credit Facility 65.0 — — BellRing Term B Facility 8.7 — — Municipal bond 1.1 — — Credit Agreement (b) — — 0.8 2020 Total $ 3,731.5 $ 49.8 $ 23.1 (a) In connection with the BellRing Amendment discussed above, BellRing paid refinancing fees. (b) In connection with the amendment and restatement of the Credit Agreement in March 2020, the Company recorded a write-off of deferred financing fees. Debt Covenants Credit Agreement Under the terms of the Credit Agreement, the Company is required to comply with a financial covenant consisting of a secured net leverage ratio (as defined in the Credit Agreement) not to exceed 4.25 to 1.00, measured as of the last day of any fiscal quarter, if, as of the last day of such fiscal quarter, the aggregate outstanding amount of all revolving credit loans, swing line loans and letter of credit obligations (subject to certain exceptions specified in the Credit Agreement) exceeds 30% of the Company’s revolving credit commitments. As of March 31, 2021, the Company was not required to comply with such financial covenant as the aggregate amount of the aforementioned obligations did not exceed 30% of the Company’s revolving credit commitments. The Credit Agreement provides for incremental revolving and term loan facilities, and also permits other secured or unsecured debt, if, among other conditions, certain financial ratios are met, as defined and specified in the Credit Agreement. BellRing Credit Agreement Under the terms of the BellRing Credit Agreement, BellRing is required to comply with a financial covenant requiring BellRing to maintain a total net leverage ratio (as defined in the BellRing Credit Agreement) not to exceed 6.00 to 1.00, measured as of the last day of each fiscal quarter. The total net leverage ratio of BellRing did not exceed this threshold as of March 31, 2021. The BellRing Credit Agreement provides for incremental revolving and term facilities, and also permits other secured or unsecured debt, if, among other conditions, certain financial ratios are met, as defined and specified in the BellRing Credit Agreement.

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	6 Months Ended
	Mar. 31, 2021
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension and Other Postretirement benefits	PENSION AND OTHER POSTRETIREMENT BENEFITSThe Company maintains qualified defined benefit plans in the U.S., the United Kingdom and Canada for certain employees primarily within its Post Consumer Brands and Weetabix segments. Certain of the Company’s employees are eligible to participate in the Company’s postretirement benefit plans (partially subsidized retiree health and life insurance). Amounts for the Canadian plans are included in the North America disclosures and are not disclosed separately because they do not constitute a significant portion of the combined amounts. The following tables provide the components of net periodic benefit cost (gain) for the pension plans. In the Condensed Consolidated Statements of Operations, service cost is reported in “Cost of goods sold” and “Selling, general and administrative expenses” and all other components of net periodic benefit cost (gain) are reported in “Other income, net.” North America Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 1.0 $ 1.0 $ 1.9 $ 2.1 Interest cost 0.8 0.9 1.6 1.8 Expected return on plan assets (1.6) (1.6) (3.2) (3.2) Recognized net actuarial loss 0.6 0.4 1.2 0.9 Recognized prior service cost — 0.1 — 0.1 Net periodic benefit cost $ 0.8 $ 0.8 $ 1.5 $ 1.7 Other International Three Months Ended Six Months Ended 2021 2020 2021 2020 Interest cost $ 3.8 $ 3.7 $ 7.5 $ 7.4 Expected return on plan assets (6.3) (6.2) (12.3) (12.4) Recognized prior service cost 0.1 — 0.2 — Net periodic benefit gain $ (2.4) $ (2.5) $ (4.6) $ (5.0) The following table provides the components of net periodic benefit gain for the North American other postretirement benefit plans. In the Condensed Consolidated Statements of Operations, service cost is reported in “Cost of goods sold” and “Selling, general and administrative expenses” and all other components of net periodic benefit cost (gain) are reported in “Other income, net.” Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 0.1 $ 0.2 $ 0.2 $ 0.3 Interest cost 0.4 0.4 0.8 0.9 Recognized net actuarial loss 0.3 0.1 0.6 0.3 Recognized prior service credit (1.2) (1.1) (2.4) (2.3) Net periodic benefit gain $ (0.4) $ (0.4) $ (0.8) $ (0.8)

Shareholders' Equity

Shareholders' Equity	6 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Shareholders' Equity	SHAREHOLDERS’ EQUITY The following table summarizes the Company’s repurchases of its common stock. Three Months Ended Six Months Ended 2021 2020 2021 2020 Shares repurchased 1.6 2.0 3.3 4.2 Average price per share $ 98.29 $ 101.77 $ 95.78 $ 102.40 Total cost including broker’s commissions (a) $ 155.4 $ 206.0 $ 315.3 $ 429.1 (a) Purchases of treasury stock in the Condensed Consolidated Statement of Cash Flows for the six months ended March 31, 2021 included $7.4 of repurchases of common stock that were accrued at September 30, 2020 and did not settle until fiscal 2021. Purchases of treasury stock in the Condensed Consolidated Statement of Cash Flows for the six months ended March 31, 2020 included $8.7 of repurchases of common stock that were accrued at September 30, 2019 and did not settle until fiscal 2020. The Company may, from time to time, enter into common stock structured repurchase arrangements with financial institutions using general corporate funds. Under such arrangements, the Company pays a fixed sum of cash upon execution of each agreement in exchange for the right to receive either a predetermined amount of cash or Post common stock. Upon expiration of each agreement, if the closing market price of Post’s common stock is above a predetermined price, the Company will have the initial investment returned with a premium in cash. If the closing market price of Post’s common stock is at or below the predetermined price, the Company will receive the number of shares specified in the agreement. During the year ended September 30, 2020, the Company entered into a structured share repurchase arrangement which required cash payments totaling $46.4, which were recorded as “Additional paid-in-capital” on the Condensed Consolidated Balance Sheet at September 30, 2020. This arrangement settled in November 2020, and the Company received cash payments of $47.5 which were recorded as “Additional paid-in-capital” on the Condensed Consolidated Balance Sheet at March 31, 2021 and as “Cash received from share repurchase contracts” in the Condensed Consolidated Statement of Cash Flows for the six months ended March 31, 2021.

Segments

Segments	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segments	SEGMENTS At March 31, 2021, the Company’s operating and reportable segments were as follows: • Post Consumer Brands: North American RTE cereal and Peter Pan nut butters; • Weetabix: primarily United Kingdom RTE cereal and muesli; • Foodservice: primarily egg and potato products; • Refrigerated Retail: primarily side dish, egg, cheese and sausage products; and • BellRing Brands: ready-to-drink (“RTD”) protein shakes, other RTD beverages, powders and nutrition bars. Due to the level of integration between the Foodservice and Refrigerated Retail segments, it is impracticable to present total assets separately for each segment. An allocation has been made between the two segments for depreciation based on inventory costing. Management evaluates each segment’s performance based on its segment profit, which for all segments excluding BellRing Brands is its earnings/loss before income taxes and equity method earnings/loss before impairment of property, goodwill and other intangible assets, facility closure related costs, restructuring expenses, gain/loss on assets and liabilities held for sale, gain/loss on sale of businesses and facilities, gain on/adjustment to bargain purchase, interest expense and other unallocated corporate income and expenses. Segment profit for BellRing Brands, as it is a publicly-traded company, is its operating profit. The following tables present information about the Company’s reportable segments. Three Months Ended Six Months Ended 2021 2020 2021 2020 Net Sales Post Consumer Brands $ 479.9 $ 507.9 $ 924.9 $ 949.1 Weetabix 113.4 113.4 226.9 214.9 Foodservice 369.2 378.4 723.7 799.0 Refrigerated Retail 239.5 237.6 502.6 487.5 BellRing Brands 282.1 257.5 564.5 501.5 Eliminations (0.8) (0.6) (1.3) (1.0) Total $ 1,483.3 $ 1,494.2 $ 2,941.3 $ 2,951.0 Segment Profit Post Consumer Brands $ 91.8 $ 92.4 $ 162.3 $ 173.0 Weetabix 25.9 28.0 54.0 51.7 Foodservice 8.8 23.8 19.6 70.8 Refrigerated Retail 24.2 30.2 57.9 56.2 BellRing Brands 15.6 35.1 63.4 84.4 Total segment profit 166.3 209.5 357.2 436.1 General corporate expenses and other 15.1 52.7 28.9 80.1 Interest expense, net 94.8 94.0 191.4 196.9 Loss on extinguishment and refinancing of debt , net 94.7 60.0 94.7 72.9 (Income) expense on swaps, net (185.6) 224.6 (227.2) 163.2 Earnings (loss) before income taxes and equity method loss $ 147.3 $ (221.8) $ 269.4 $ (77.0) Net sales by product Cereal and granola $ 575.7 $ 621.1 $ 1,134.0 $ 1,163.6 Nut butters 17.4 — 17.4 — Eggs and egg products 353.8 363.2 691.9 758.5 Side dishes (including potato products) 138.4 143.1 293.9 291.6 Cheese and dairy 54.6 56.5 117.3 124.1 Sausage 43.0 40.3 87.3 86.2 Protein-based products and supplements 282.2 257.6 564.7 501.7 Other 18.8 12.9 35.8 26.1 Eliminations (0.6) (0.5) (1.0) (0.8) Total $ 1,483.3 $ 1,494.2 $ 2,941.3 $ 2,951.0 Depreciation and amortization Post Consumer Brands $ 29.2 $ 28.1 $ 57.4 $ 56.0 Weetabix 9.4 8.6 18.8 17.3 Foodservice 31.6 29.7 62.3 58.7 Refrigerated Retail 18.3 17.6 36.4 35.0 BellRing Brands 23.9 6.4 30.6 12.8 Total segment depreciation and amortization 112.4 90.4 205.5 179.8 Corporate 1.0 1.1 2.0 2.0 Total $ 113.4 $ 91.5 $ 207.5 $ 181.8 Assets March 31, September 30, Post Consumer Brands $ 3,407.9 $ 3,291.7 Weetabix 1,983.3 1,864.5 Foodservice and Refrigerated Retail 5,096.9 5,022.0 BellRing Brands 639.2 653.5 Corporate 1,013.7 1,315.0 Total $ 12,141.0 $ 12,146.7

Noncontrolling Interests, Equ_2

Noncontrolling Interests, Equity Interests and Related Party Transactions (Tables)	6 Months Ended
	Mar. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Effects of changes in ownership of BellRing on Post equity	Three Months Ended Six Months Ended 2021 2020 2021 2020 Increase in additional paid-in capital related to net proceeds from BellRing IPO $ — $ — $ — $ 524.4 (Decrease) increase in additional paid-in capital related to establishment of noncontrolling interest — (1.4) — 64.9 Decrease in additional paid-in capital related to tax effects of BellRing IPO — — — (133.7) Net transfers (to) from NCI $ — $ (1.4) $ — $ 455.6
Equity method loss attributable to 8th Avenue	Three Months Ended Six Months Ended 2021 2020 2021 2020 8th Avenue’s net loss available to 8th Avenue’s common shareholders $ (8.5) $ (15.2) $ (18.7) $ (23.9) 60.5 % 60.5 % 60.5 % 60.5 % Equity method loss available to Post $ (5.1) $ (9.2) $ (11.3) $ (14.5) Less: Amortization of basis difference, net of tax (a) 1.7 1.7 3.4 3.4 Equity method loss, net of tax $ (6.8) $ (10.9) $ (14.7) $ (17.9)
8th Avenue Summarized Financial Information	Three Months Ended Six Months Ended 2021 2020 2021 2020 Net sales $ 220.7 $ 233.1 $ 449.7 $ 451.5 Gross profit $ 34.3 $ 41.2 $ 69.7 $ 79.6 Net earnings (loss) $ 0.3 $ (7.2) $ (1.1) $ (8.1) Less: Preferred stock dividend 8.8 8.0 17.6 15.8 Net Loss Available to 8th Avenue Common Shareholders $ (8.5) $ (15.2) $ (18.7) $ (23.9)

Business Combinations (Tables)

Business Combinations (Tables)	6 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Opening Balance Sheets	Peter Pan Almark Receivables $ — $ 6.4 Inventories 4.6 5.2 Prepaid expenses and other current assets — 0.1 Property — 9.8 Goodwill 55.1 19.7 Other intangible assets 67.0 19.5 Deferred tax asset — 1.3 Other assets — 32.9 Accounts payable (11.7) (5.4) Other current liabilities — (1.6) Deferred tax liability (13.6) — Other liabilities — (36.6) Total acquisition cost $ 101.4 $ 51.3
Pro Forma Information	Three Months Ended Six Months Ended 2021 2020 2021 2020 Pro forma net sales $ 1,494.3 $ 1,549.9 $ 2,985.9 $ 3,060.4 Pro forma net earnings (loss) available to common shareholders $ 110.5 $ (188.0) $ 191.9 $ (94.1) Pro forma basic earnings (loss) per common share $ 1.72 $ (2.71) $ 2.96 $ (1.34) Pro forma diluted earnings (loss) per common share $ 1.70 $ (2.71) $ 2.91 $ (1.34)

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Mar. 31, 2021
Restructuring [Abstract]
Restructuring charges and related liabilities	Balance, September 30, 2020 $ — Charge to expense 4.8 Cash payments (3.7) Non-cash charges — Balance, March 31, 2021 $ 1.1 Total expected restructuring charges $ 4.9 Cumulative restructuring charges incurred to date 4.8 Remaining expected restructuring charges $ 0.1

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Computation of basic and diluted earnings (loss) per share	Three Months Ended Six Months Ended 2021 2020 2021 2020 Net earnings (loss) for basic earnings (loss) per share $ 109.9 $ (191.4) $ 191.1 $ (92.2) Dilutive impact of BellRing net earnings — — — — Net earnings (loss) for diluted earnings (loss) per share $ 109.9 $ (191.4) $ 191.1 $ (92.2) Weighted-average shares for basic earnings (loss) per share 64.1 69.3 64.9 70.0 Effect of dilutive securities: Stock options 0.6 — 0.6 — Stock appreciation rights 0.1 — 0.1 — Restricted stock units 0.2 — 0.3 — Performance-based restricted stock units 0.1 — 0.1 — Total dilutive securities 1.0 — 1.1 — Weighted-average shares for diluted earnings (loss) per share 65.1 69.3 66.0 70.0 Basic earnings (loss) per common share $ 1.71 $ (2.76) $ 2.94 $ (1.32) Diluted earnings (loss) per common share $ 1.69 $ (2.76) $ 2.90 $ (1.32)
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share
Antidilutive Securities Excluded from Computation of Diluted Earnings (Loss) Per Share	Three Months Ended Six Months Ended 2021 2020 2021 2020 Stock options 0.1 1.7 0.1 1.7 Stock appreciation rights — 0.1 — 0.1 Restricted stock units — 1.0 — 1.0 Performance-based restricted stock units 0.1 0.2 0.1 0.2

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Mar. 31, 2021
Inventory [Abstract]
Inventories	March 31, September 30, Raw materials and supplies $ 112.3 $ 118.1 Work in process 19.7 17.8 Finished products 471.7 429.4 Flocks 36.0 34.1 $ 639.7 $ 599.4

Property, net (Tables)

Property, net (Tables)	6 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, net	March 31, September 30, Property, at cost $ 3,073.3 $ 2,979.2 Accumulated depreciation (1,296.7) (1,199.5) $ 1,776.6 $ 1,779.7

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2021
Goodwill
Carrying Amount of Goodwill	Post Consumer Brands Weetabix Foodservice Refrigerated Retail BellRing Brands Total Balance, September 30, 2020 Goodwill (gross) $ 2,011.8 $ 889.5 $ 1,335.6 $ 793.6 $ 180.7 $ 5,211.2 Accumulated impairment losses (609.1) — — (48.7) (114.8) (772.6) Goodwill (net) $ 1,402.7 $ 889.5 $ 1,335.6 $ 744.9 $ 65.9 $ 4,438.6 Goodwill acquired 55.1 — 19.7 — — 74.8 Currency translation adjustment 0.2 61.0 — — — 61.2 Balance, March 31, 2021 Goodwill (gross) $ 2,067.1 $ 950.5 $ 1,355.3 $ 793.6 $ 180.7 $ 5,347.2 Accumulated impairment losses (609.1) — — (48.7) (114.8) (772.6) Goodwill (net) $ 1,458.0 $ 950.5 $ 1,355.3 $ 744.9 $ 65.9 $ 4,574.6

Intangible Assets, net (Tables)

Intangible Assets, net (Tables)	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Total Intangible Assets	March 31, 2021 September 30, 2020 Carrying Accumulated Net Carrying Accumulated Net Subject to amortization: Customer relationships $ 2,348.1 $ (754.8) $ 1,593.3 $ 2,304.8 $ (681.9) $ 1,622.9 Trademarks and brands 852.0 (295.6) 556.4 795.0 (266.9) 528.1 Other intangible assets 3.1 (3.1) — 3.1 (3.1) — 3,203.2 (1,053.5) 2,149.7 3,102.9 (951.9) 2,151.0 Not subject to amortization: Trademarks and brands 1,064.5 — 1,064.5 1,046.5 — 1,046.5 $ 4,267.7 $ (1,053.5) $ 3,214.2 $ 4,149.4 $ (951.9) $ 3,197.5

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging (Tables)	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional amounts of derivatives held		March 31, September 30, Commodity contracts $ 36.7 $ 24.7 Energy contracts 65.9 87.1 Foreign exchange contracts - Forward contracts 20.9 28.9 Interest rate swaps 620.9 621.7 Interest rate swaps - Rate-lock swaps 1,609.8 1,666.0 Interest rate swaps - Options 433.3 433.3
Derivative Instruments in Condensed Consolidated Balance Sheets		Balance Sheet Location March 31, September 30, Asset Derivatives: Commodity contracts Prepaid expenses and other current assets $ 8.2 $ 5.0 Energy contracts Prepaid expenses and other current assets 5.2 1.8 Commodity contracts Other assets 6.0 0.1 Energy contracts Other assets 4.1 0.9 Foreign exchange contracts Prepaid expenses and other current assets — 0.1 Interest rate swaps Prepaid expenses and other current assets — 6.8 Interest rate swaps Other assets 40.0 — $ 63.5 $ 14.7 Liability Derivatives: Commodity contracts Other current liabilities $ 0.6 $ 1.4 Energy contracts Other current liabilities — 10.1 Energy contracts Other liabilities — 3.9 Foreign exchange contracts Other current liabilities 1.1 — Interest rate swaps Other current liabilities 68.4 176.4 Interest rate swaps Other liabilities 247.8 351.3 $ 317.9 $ 543.1
Effect of Derivative Instruments on the Condensed Consolidated Statements of Operations and Condensed Consolidated Statements of Other Comprehensive Income	The following tables present the effects of the Company’s derivative instruments on the Condensed Consolidated Statements of Operations and Condensed Consolidated Statements of Comprehensive Income (Loss) for the three months ended March 31, 2021 and 2020. Derivatives Not Designated as Hedging Instruments Statement of Operations Location (Gain) Loss Recognized in Statement of Operations 2021 2020 Commodity contracts Cost of goods sold $ (2.3) $ 8.0 Energy contracts Cost of goods sold (11.3) 26.0 Foreign exchange contracts Selling, general and administrative expenses (0.3) (0.1) Interest rate swaps Interest expense, net 0.5 — Interest rate swaps (Income) expense on swaps, net (185.6) 224.6 Derivatives Designated as Hedging Instruments Loss (Gain) Recognized in OCI including NCI Loss (Gain) Reclassified from Accumulated OCI including NCI into Earnings (a) Statement of Operations Location 2021 2020 2021 2020 Interest rate swaps $ — $ 11.0 $ 0.6 $ (0.2) Interest expense, net Cross-currency swaps — (66.8) — — (Income) expense on swaps, net	The following tables present the effects of the Company’s derivative instruments on the Condensed Consolidated Statements of Operations and Condensed Consolidated Statements of Comprehensive Income (Loss) for the six months ended March 31, 2021 and 2020. Derivatives Not Designated as Hedging Instruments Statement of Operations Location (Gain) Loss Recognized in Statement of Operations 2021 2020 Commodity contracts Cost of goods sold $ (9.7) $ 6.1 Energy contracts Cost of goods sold (19.3) 23.5 Foreign exchange contracts Selling, general and administrative expenses 1.2 (0.1) Interest rate swaps Interest expense, net 1.0 — Interest rate swaps (Income) expense on swaps, net (227.2) 163.2 Derivatives Designated as Hedging Instruments Loss (Gain) Recognized in OCI including NCI Loss Reclassified from Accumulated OCI including NCI into Earnings (a) Statement of Operations Location 2021 2020 2021 2020 Interest rate swaps $ — $ 9.7 1.1 7.0 Interest expense, net Cross-currency swaps — (32.2) — — (Income) expense on swaps, net (a) For the six months ended March 31, 2021, this amount includes the amortization of previously unrealized losses on BellRing’s interest rate swaps that were de-designated as hedging instruments as of April 1, 2020. For the six
Net Hedging (Gains) Losses on Interest Rate Swaps	The following table presents the components of the Company’s net hedging (gains) losses on interest rate swaps, which are included in “Interest expense, net” and “(Income) expense on swaps, net” in the Condensed Consolidated Statements of Operations, as well as cash settlements paid (received) during the periods presented. Three Months Ended Statement of Operations Location Mark-to-Market (Gain) Loss, net Net Loss Reclassified from Accumulated OCI including NCI (a) Total Net Hedging (Gain) Loss Cash Settlements Paid (Received), Net Interest expense, net $ (0.1) $ 0.6 $ 0.5 $ 1.2 (Income) expense on swaps, net (185.6) — (185.6) 13.6 2021 Total $ (185.7) $ 0.6 $ (185.1) $ 14.8 Interest expense, net $ (0.2) $ — $ (0.2) $ (0.2) (Income) expense on swaps, net 224.6 — 224.6 0.4 2020 Total $ 224.4 $ — $ 224.4 $ 0.2 (a) Includes the amortization of previously unrealized losses on BellRing’s interest rate swaps over the term of the related debt that were de-designated as hedging instruments, as well as the reclassification of previously unrealized losses on interest rate swaps that were de-designated as hedging instruments.	The following table presents the components of the Company’s net hedging (gains) losses on interest rate swaps, which are included in “Interest expense, net” and “(Income) expense on swaps, net” in the Condensed Consolidated Statements of Operations, as well as cash settlements paid (received) during the periods presented. Six Months Ended Statement of Operations Location Mark-to-Market (Gain) Loss, net Net Loss Reclassified from Accumulated OCI including NCI (a) Total Net Hedging (Gain) Loss Cash Settlements Paid (Received), Net Interest expense, net $ (0.1) $ 1.1 $ 1.0 $ 2.4 (Income) expense on swaps, net (227.2) — (227.2) 15.1 2021 Total $ (227.3) $ 1.1 $ (226.2) $ 17.5 Interest expense, net $ (0.2) $ 7.2 $ 7.0 $ (0.2) (Income) expense on swaps, net 163.2 — 163.2 19.5 2020 Total $ 163.0 $ 7.2 $ 170.2 $ 19.3 (a) Includes the amortization of previously unrealized losses on BellRing’s interest rate swaps over the term of the related debt that were de-designated as hedging instruments, as well as the reclassification of previously unrealized losses on interest rate swaps that were de-designated as hedging instruments.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Mar. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets and liabilities measured at fair value on a recurring basis	March 31, 2021 September 30, 2020 Total Level 1 Level 2 Total Level 1 Level 2 Assets: Deferred compensation investments $ 14.8 $ 14.8 $ — $ 12.8 $ 12.8 $ — Derivative assets 63.5 — 63.5 14.7 — 14.7 Equity securities 46.7 46.7 — 27.9 27.9 — $ 125.0 $ 61.5 $ 63.5 $ 55.4 $ 40.7 $ 14.7 Liabilities: Deferred compensation liabilities $ 34.0 $ — $ 34.0 $ 29.7 $ — $ 29.7 Derivative liabilities 317.9 — 317.9 543.1 — 543.1 $ 351.9 $ — $ 351.9 $ 572.8 $ — $ 572.8
Assets and liabilities measured at fair value on a nonrecurring basis	Balance, September 30, 2020 $ 7.3 Net gain related to assets held for sale 0.5 Proceeds from the sale of assets held for sale (7.9) Currency translation adjustment 0.1 Balance, March 31, 2021 $ —

Leases (Tables)

Leases (Tables)	6 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Balance Sheet location of Operating Leases	March 31, September 30, ROU assets: Other assets $ 141.1 $ 116.3 Lease liabilities: Other current liabilities $ 25.8 $ 23.6 Other liabilities 130.2 103.0 Total lease liabilities $ 156.0 $ 126.6
Maturities of Lease Liabilities	March 31, Remaining Fiscal 2021 $ 16.0 Fiscal 2022 31.3 Fiscal 2023 27.8 Fiscal 2024 21.0 Fiscal 2025 14.9 Thereafter 79.6 Total future minimum payments $ 190.6 Less: Implied interest 34.6 Total lease liabilities $ 156.0
Supplemental Operations Statement Information	Three Months Ended Six Months Ended 2021 2020 2021 2020 Operating lease expense $ 11.0 $ 10.1 $ 21.4 $ 21.1 Variable lease expense 1.2 1.3 2.7 2.5 Short-term lease expense 2.0 1.7 3.6 3.7

Long-Term Debt (Tables)

Long-Term Debt (Tables)	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Long-term Debt	March 31, September 30, 4.50% Senior Notes maturing September 2031 $ 1,800.0 $ — 4.625% Senior Notes maturing April 2030 1,650.0 1,650.0 5.50% Senior Notes maturing December 2029 750.0 750.0 5.625% Senior Notes maturing January 2028 940.9 940.9 5.75% Senior Notes maturing March 2027 1,299.3 1,299.3 5.00% Senior Notes maturing August 2026 — 1,697.3 BellRing Term B Facility 627.4 673.7 BellRing Revolving Credit Facility — 30.0 Municipal bond 7.5 8.5 $ 7,075.1 $ 7,049.7 Less: Current portion of long-term debt 74.3 64.9 Debt issuance costs, net 55.7 62.6 Plus: Unamortized premium and discount, net 35.9 36.8 Total long-term debt $ 6,981.0 $ 6,959.0
Repayments of Long-term Debt	Three Months Ended Repayments of Long-Term Debt Loss on Extinguishment and Refinancing of Debt, net Issuance or Borrowing Principal Amount Repaid Debt Premiums and Refinancing Fees Paid Write-off of Debt Issuance Costs and Deferred Financing Fees 5.00% Senior Notes $ 1,697.3 $ 74.3 $ 18.9 BellRing Revolving Credit Facility 50.0 — — BellRing Term B Facility 8.8 — — Municipal bond 1.0 — — BellRing Credit Agreement (a) — 1.5 — 2021 Total $ 1,757.1 $ 75.8 $ 18.9 5.50% Senior Notes maturing in March 2025 $ 1,000.0 $ 41.3 $ 8.7 8.00% Senior Notes 122.2 8.5 0.7 BellRing Revolving Credit Facility 25.0 — — BellRing Term B Facility 8.7 — — Municipal bond 1.1 — — Credit Agreement (b) — — 0.8 2020 Total $ 1,157.0 $ 49.8 $ 10.2 Six Months Ended Repayments of Long-Term Debt Loss on Extinguishment and Refinancing of Debt, net Issuance or Borrowing Principal Amount Repaid Debt Premiums and Refinancing Fees Paid Write-off of Debt Issuance Costs and Deferred Financing Fees 5.00% Senior Notes $ 1,697.3 $ 74.3 $ 18.9 BellRing Revolving Credit Facility 50.0 — — BellRing Term B Facility 46.3 — — Municipal bond 1.0 — — BellRing Credit Agreement (a) — 1.5 — 2021 Total $ 1,794.6 $ 75.8 $ 18.9 Term loan $ 1,309.5 $ — $ 9.1 Bridge loan 1,225.0 — 3.8 5.50% Senior Notes maturing in March 2025 1,000.0 41.3 8.7 8.00% Senior Notes 122.2 8.5 0.7 BellRing Revolving Credit Facility 65.0 — — BellRing Term B Facility 8.7 — — Municipal bond 1.1 — — Credit Agreement (b) — — 0.8 2020 Total $ 3,731.5 $ 49.8 $ 23.1 (a) In connection with the BellRing Amendment discussed above, BellRing paid refinancing fees. (b) In connection with the amendment and restatement of the Credit Agreement in March 2020, the Company recorded a write-off of deferred financing fees.

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits (Tables)	6 Months Ended
	Mar. 31, 2021
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Components of net periodic benefit cost (gain)	The following tables provide the components of net periodic benefit cost (gain) for the pension plans. In the Condensed Consolidated Statements of Operations, service cost is reported in “Cost of goods sold” and “Selling, general and administrative expenses” and all other components of net periodic benefit cost (gain) are reported in “Other income, net.” North America Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 1.0 $ 1.0 $ 1.9 $ 2.1 Interest cost 0.8 0.9 1.6 1.8 Expected return on plan assets (1.6) (1.6) (3.2) (3.2) Recognized net actuarial loss 0.6 0.4 1.2 0.9 Recognized prior service cost — 0.1 — 0.1 Net periodic benefit cost $ 0.8 $ 0.8 $ 1.5 $ 1.7 Other International Three Months Ended Six Months Ended 2021 2020 2021 2020 Interest cost $ 3.8 $ 3.7 $ 7.5 $ 7.4 Expected return on plan assets (6.3) (6.2) (12.3) (12.4) Recognized prior service cost 0.1 — 0.2 — Net periodic benefit gain $ (2.4) $ (2.5) $ (4.6) $ (5.0) The following table provides the components of net periodic benefit gain for the North American other postretirement benefit plans. In the Condensed Consolidated Statements of Operations, service cost is reported in “Cost of goods sold” and “Selling, general and administrative expenses” and all other components of net periodic benefit cost (gain) are reported in “Other income, net.” Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 0.1 $ 0.2 $ 0.2 $ 0.3 Interest cost 0.4 0.4 0.8 0.9 Recognized net actuarial loss 0.3 0.1 0.6 0.3 Recognized prior service credit (1.2) (1.1) (2.4) (2.3) Net periodic benefit gain $ (0.4) $ (0.4) $ (0.8) $ (0.8)

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	6 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Repurchases of Common Stock	Three Months Ended Six Months Ended 2021 2020 2021 2020 Shares repurchased 1.6 2.0 3.3 4.2 Average price per share $ 98.29 $ 101.77 $ 95.78 $ 102.40 Total cost including broker’s commissions (a) $ 155.4 $ 206.0 $ 315.3 $ 429.1 (a) Purchases of treasury stock in the Condensed Consolidated Statement of Cash Flows for the six months ended March 31, 2021 included $7.4 of repurchases of common stock that were accrued at September 30, 2020 and did not settle until fiscal 2021. Purchases of treasury stock in the Condensed Consolidated Statement of Cash Flows for the six months ended March 31, 2020 included $8.7 of repurchases of common stock that were accrued at September 30, 2019 and did not settle until fiscal 2020.

Segments (Tables)

Segments (Tables)	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segment Reporting Information, by Segment and Disaggregated Revenue	Three Months Ended Six Months Ended 2021 2020 2021 2020 Net Sales Post Consumer Brands $ 479.9 $ 507.9 $ 924.9 $ 949.1 Weetabix 113.4 113.4 226.9 214.9 Foodservice 369.2 378.4 723.7 799.0 Refrigerated Retail 239.5 237.6 502.6 487.5 BellRing Brands 282.1 257.5 564.5 501.5 Eliminations (0.8) (0.6) (1.3) (1.0) Total $ 1,483.3 $ 1,494.2 $ 2,941.3 $ 2,951.0 Segment Profit Post Consumer Brands $ 91.8 $ 92.4 $ 162.3 $ 173.0 Weetabix 25.9 28.0 54.0 51.7 Foodservice 8.8 23.8 19.6 70.8 Refrigerated Retail 24.2 30.2 57.9 56.2 BellRing Brands 15.6 35.1 63.4 84.4 Total segment profit 166.3 209.5 357.2 436.1 General corporate expenses and other 15.1 52.7 28.9 80.1 Interest expense, net 94.8 94.0 191.4 196.9 Loss on extinguishment and refinancing of debt , net 94.7 60.0 94.7 72.9 (Income) expense on swaps, net (185.6) 224.6 (227.2) 163.2 Earnings (loss) before income taxes and equity method loss $ 147.3 $ (221.8) $ 269.4 $ (77.0) Net sales by product Cereal and granola $ 575.7 $ 621.1 $ 1,134.0 $ 1,163.6 Nut butters 17.4 — 17.4 — Eggs and egg products 353.8 363.2 691.9 758.5 Side dishes (including potato products) 138.4 143.1 293.9 291.6 Cheese and dairy 54.6 56.5 117.3 124.1 Sausage 43.0 40.3 87.3 86.2 Protein-based products and supplements 282.2 257.6 564.7 501.7 Other 18.8 12.9 35.8 26.1 Eliminations (0.6) (0.5) (1.0) (0.8) Total $ 1,483.3 $ 1,494.2 $ 2,941.3 $ 2,951.0 Depreciation and amortization Post Consumer Brands $ 29.2 $ 28.1 $ 57.4 $ 56.0 Weetabix 9.4 8.6 18.8 17.3 Foodservice 31.6 29.7 62.3 58.7 Refrigerated Retail 18.3 17.6 36.4 35.0 BellRing Brands 23.9 6.4 30.6 12.8 Total segment depreciation and amortization 112.4 90.4 205.5 179.8 Corporate 1.0 1.1 2.0 2.0 Total $ 113.4 $ 91.5 $ 207.5 $ 181.8 Assets March 31, September 30, Post Consumer Brands $ 3,407.9 $ 3,291.7 Weetabix 1,983.3 1,864.5 Foodservice and Refrigerated Retail 5,096.9 5,022.0 BellRing Brands 639.2 653.5 Corporate 1,013.7 1,315.0 Total $ 12,141.0 $ 12,146.7

Noncontrolling Interests, Equ_3

Noncontrolling Interests, Equity Interests and Related Party Transactions (Details) $ / shares in Units, shares in Millions, $ in Millions	Oct. 21, 2019USD ($)$ / sharesshares	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Oct. 01, 2018USD ($)
Schedule of Equity Method Investments
Proceeds from initial public offering				$ 0	$ 524.4
Equity method earnings (loss), net of tax		$ (7)	$ (11.1)	(14.9)	(18.4)
Equity method investments		99.7		$ 99.7		$ 114.1
Number of Joint Ventures Held				2
8th Avenue
Schedule of Equity Method Investments
Net Loss Available to 8th Avenue Common Shareholders		$ (8.5)	$ (15.2)	$ (18.7)	$ (23.9)
Equity Method Investment, Ownership Percentage		60.50%	60.50%	60.50%	60.50%
Equity method loss available to Common Shareholders		$ (5.1)	$ (9.2)	$ (11.3)	$ (14.5)
Amortization of basis difference, net of tax		1.7	1.7	3.4	3.4
Equity method earnings (loss), net of tax		(6.8)	(10.9)	(14.7)	(17.9)
Total Basis Difference Recognized							$ 70.3
Remaining Basis Difference to be Amortized		51.2		51.2		54.6
Net sales		220.7	233.1	449.7	451.5
Gross profit		34.3	41.2	69.7	79.6
Net earnings (loss)		0.3	(7.2)	(1.1)	(8.1)
Less: Preferred stock dividend		8.8	8	17.6	15.8
Revenue from Related Parties		2	1.6	4	3.2
Purchases from and Royalties paid to Related Party		$ 15.4	2.4	$ 17.6	5.2
Alpen Food Company South Africa (Pty) Limited
Schedule of Equity Method Investments
Equity Method Investment, Ownership Percentage		50.00%		50.00%
Equity method earnings (loss), net of tax		$ (0.2)	(0.2)	$ (0.2)	(0.5)
Equity Method Investments | 8th Avenue
Schedule of Equity Method Investments
Equity method investments		95.4		95.4		110.1
Equity Method Investments | Alpen Food Company South Africa (Pty) Limited
Schedule of Equity Method Investments
Equity method investments		4.3		4.3		4
Accounts Receivable | 8th Avenue
Schedule of Equity Method Investments
Accounts Receivable, Related Parties		4.7		4.7		3.2
Accounts Payable | 8th Avenue
Schedule of Equity Method Investments
Accounts Payable, Related Parties		5.5		5.5		0.6
Other Liabilities | 8th Avenue
Schedule of Equity Method Investments
Due to Related Parties		0.7		0.7		0.7
Other Assets | Alpen Food Company South Africa (Pty) Limited
Schedule of Equity Method Investments
Notes Receivable, Related Parties, Noncurrent		0.5		0.5		$ 0.5
Selling, General and Administrative Expenses | 8th Avenue
Schedule of Equity Method Investments
MSA and Advisory Income		$ 0.8	1	$ 1.6	2
BellRing Brands, LLC | BellRing Brands, Inc.
Schedule of Equity Method Investments
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	28.80%	28.80%		28.80%		28.80%
BellRing Brands, LLC | Post Holdings, Inc.
Schedule of Equity Method Investments
Noncontrolling Interest, Ownership Percentage by Parent	71.20%	71.20%		71.20%		71.20%
Post Holdings, Inc. | Weetabix East Africa Limited
Schedule of Equity Method Investments
Noncontrolling Interest, Ownership Percentage by Parent		50.10%		50.10%
Additional Paid-in Capital
Schedule of Equity Method Investments
Net transfers (to) from NCI		$ 0	(1.4)	$ 0	455.6
Additional Paid-in Capital | BellRing
Schedule of Equity Method Investments
Proceeds from initial public offering		0	0	0	524.4
(Decrease) increase in additional paid-in capital related to establishment of noncontrolling interest		0	(1.4)	0	64.9
Decrease in additional paid-in capital related to tax effects of BellRing IPO		0	0	0	(133.7)
Net transfers (to) from NCI		$ 0	$ (1.4)	$ 0	$ 455.6
Minimum | BellRing Brands, LLC | Post Holdings, Inc.
Schedule of Equity Method Investments
Noncontrolling Interest, Ownership Percentage by Parent	50.00%
Common Class A | BellRing Brands, Inc.
Schedule of Equity Method Investments
Common Stock, Shares, Issued | shares	39.4
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01
Proceeds from initial public offering	$ 524.4
Common Class B | BellRing Brands, Inc.
Schedule of Equity Method Investments
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01
Initial Public Offering, Percentage of Voting Interests	67.00%

Business Combinations (Details)

Business Combinations (Details) - USD ($) $ in Millions	Feb. 01, 2021	Jan. 25, 2021	Jul. 01, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Business Acquisition
Net Sales				$ 1,483.3	$ 1,494.2	$ 2,941.3	$ 2,951
Operating Profit				145.1	$ 153.5	311.4	$ 349.5
Goodwill				4,574.6		4,574.6		$ 4,438.6
Peter Pan
Business Acquisition
Payments to Acquire Businesses, Base Purchase Price		$ 102
Payment at closing		$ 103.4
Net Sales				17.4		17.4
Operating Profit				3.5		3.5
Receivables				0		0
Inventories				4.6		4.6
Prepaid expenses and other current assets				0		0
Property				0		0
Goodwill				55.1		55.1
Other intangible assets				67		67
Deferred tax asset				0		0
Other assets				0		0
Accounts payable				(11.7)		(11.7)
Other current liabilities				0		0
Deferred tax liability				(13.6)		(13.6)
Other liabilities				0		0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net				101.4		101.4
Peter Pan | Receivables, net
Business Acquisition
Receivables				2		$ 2
Peter Pan | Customer Relationships
Business Acquisition
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						20 years
Other intangible assets				12		$ 12
Peter Pan | Trademarks and Brands
Business Acquisition
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						20 years
Other intangible assets				55		$ 55
Almark Foods
Business Acquisition
Payments to Acquire Businesses, Base Purchase Price	$ 52
Payment at closing	$ 51.3
Net Sales				14.4		14.4
Operating Profit				0.1		0.1
Receivables				6.4		6.4
Inventories				5.2		5.2
Prepaid expenses and other current assets				0.1		0.1
Property				9.8		9.8
Goodwill				19.7		19.7
Other intangible assets				19.5		19.5
Deferred tax asset				1.3		1.3
Other assets				32.9		32.9
Accounts payable				(5.4)		(5.4)
Other current liabilities				(1.6)		(1.6)
Deferred tax liability				0		0
Other liabilities				(36.6)		(36.6)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net				51.3		$ 51.3
Almark Foods | Customer Relationships
Business Acquisition
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						10 years
Other intangible assets				19.5		$ 19.5
Henningsen Foods
Business Acquisition
Payments to Acquire Businesses, Base Purchase Price			$ 20
Payment at closing			$ 22.7
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net								32.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents								2.8
Business Combination, Bargain Purchase, Gain Recognized, Amount								11.7
Business Combination, Working Capital Receivable								$ 1.8
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory and Deferred Income Taxes				2.2		0.7
Business acquisitions, net of cash acquired						1
Business Combination, Adjustment to Bargain Purchase, Gain (Loss)				$ 2.2		$ (0.1)

Business Combinations Pro Forma

Business Combinations Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Business Combinations [Abstract]
Pro forma net sales	$ 1,494.3	$ 1,549.9	$ 2,985.9	$ 3,060.4
Pro forma net earnings (loss) available to common shareholders	$ 110.5	$ (188)	$ 191.9	$ (94.1)
Pro forma basic earnings (loss) per share (in usd per share)	$ 1.72	$ (2.71)	$ 2.96	$ (1.34)
Pro forma diluted earnings (loss) per share (in usd per share)	$ 1.70	$ (2.71)	$ 2.91	$ (1.34)

Restructuring (Details)

Restructuring (Details) - Employee Severance $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2021USD ($)
Restructuring Reserve
Balance, Beginning of Period		$ 0
Charge to expense	$ 0.3	4.8
Cash payments		(3.7)
Non-cash charges		0
Balance, End of Period	1.1	1.1
Total expected restructuring charges	4.9	4.9
Cumulative restructuring charges incurred to date	4.8	4.8
Remaining expected restructuring charges	$ 0.1	$ 0.1

Amounts Held for Sale (Details)

Amounts Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Gain) loss on assets held for sale	$ 0.1	$ (0.5)
Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Gain) loss on assets held for sale		(0.5)
Post Consumer Brands | Clinton, Massachusetts facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, net			$ 3.4
(Gain) loss on assets held for sale	$ 0.1	0.1
Post Consumer Brands | Asheboro, North Carolina facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, net			1.4
(Gain) loss on assets held for sale		0.1
Weetabix Segment | Corby, United Kingdom facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, net			$ 2.5
(Gain) loss on assets held for sale		$ (0.7)

Earnings (Loss) Per Share (Deta

Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Earnings (Loss) Per Share, Diluted, by Common Class, Including Two Class Method
Net earnings (loss) for basic earnings (loss) per share	$ 109.9	$ (191.4)	$ 191.1	$ (92.2)
Dilutive impact of BellRing net earnings	0	0	0	0
Net earnings (loss) for diluted earnings (loss) per share	$ 109.9	$ (191.4)	$ 191.1	$ (92.2)
Weighted-average shares for basic earnings per share	64.1	69.3	64.9	70
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1	0	1.1	0
Weighted-average shares for diluted earnings (loss) per share	65.1	69.3	66	70
Basic earnings (loss) per share (in usd per share)	$ 1.71	$ (2.76)	$ 2.94	$ (1.32)
Diluted earnings (loss) per share (in usd per share)	$ 1.69	$ (2.76)	$ 2.90	$ (1.32)
Stock Options
Earnings (Loss) Per Share, Diluted, by Common Class, Including Two Class Method
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.6	0	0.6	0
Stock Appreciation Rights
Earnings (Loss) Per Share, Diluted, by Common Class, Including Two Class Method
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.1	0	0.1	0
Restricted Stock Awards
Earnings (Loss) Per Share, Diluted, by Common Class, Including Two Class Method
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.2	0	0.3	0
Performance-based restricted stock awards
Earnings (Loss) Per Share, Diluted, by Common Class, Including Two Class Method
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.1	0	0.1	0

Earnings (Loss) Per Share Antid

Earnings (Loss) Per Share Antidilutive shares excluded from earnings per share (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Stock Options
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share, Amount	0.1	1.7	0.1	1.7
Stock Appreciation Rights
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share, Amount	0	0.1	0	0.1
Restricted Stock Awards
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share, Amount	0	1	0	1
Performance-based restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share
Antidilutive Securities Excluded from Computation of Earnings (Loss) Per Share, Amount	0.1	0.2	0.1	0.2

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Inventory [Abstract]
Raw materials and supplies	$ 112.3	$ 118.1
Work in process	19.7	17.8
Finished products	471.7	429.4
Flocks	36	34.1
Inventories	$ 639.7	$ 599.4

Property, net (Details)

Property, net (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Property, at cost	$ 3,073.3	$ 2,979.2
Accumulated depreciation	(1,296.7)	(1,199.5)
Property, net	$ 1,776.6	$ 1,779.7

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Goodwill
Goodwill (gross)	$ 5,347.2	$ 5,211.2
Accumulated impairment losses	(772.6)	(772.6)
Goodwill	4,574.6	4,438.6
Goodwill acquired	74.8
Currency translation adjustment	61.2
Post Consumer Brands
Goodwill
Goodwill (gross)	2,067.1	2,011.8
Accumulated impairment losses	(609.1)	(609.1)
Goodwill	1,458	1,402.7
Goodwill acquired	55.1
Currency translation adjustment	0.2
Weetabix
Goodwill
Goodwill (gross)	950.5	889.5
Accumulated impairment losses	0	0
Goodwill	950.5	889.5
Goodwill acquired	0
Currency translation adjustment	61
Foodservice
Goodwill
Goodwill (gross)	1,355.3	1,335.6
Accumulated impairment losses	0	0
Goodwill	1,355.3	1,335.6
Goodwill acquired	19.7
Currency translation adjustment	0
Refrigerated Retail
Goodwill
Goodwill (gross)	793.6	793.6
Accumulated impairment losses	(48.7)	(48.7)
Goodwill	744.9	744.9
Goodwill acquired	0
Currency translation adjustment	0
BellRing Brands
Goodwill
Goodwill (gross)	180.7	180.7
Accumulated impairment losses	(114.8)	(114.8)
Goodwill	65.9	$ 65.9
Goodwill acquired	0
Currency translation adjustment	$ 0

Intangible Assets, net (Details

Intangible Assets, net (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Gross	$ 3,203.2	$ 3,203.2	$ 3,102.9
Finite-Lived Intangible Assets, Accumulated Amortization	(1,053.5)	(1,053.5)	(951.9)
Finite-Lived Intangible Assets, Net	2,149.7	2,149.7	2,151
Intangible Assets, Net (Excluding Goodwill)
Carrying amount, total	4,267.7	4,267.7	4,149.4
Other intangible assets, net	3,214.2	3,214.2	3,197.5
Supreme Protein
Intangible Assets, Net (Excluding Goodwill)
Accelerated Amortization	17.7	18.1
Trademarks and brands
Indefinite-Lived Intangible Assets (Excluding Goodwill)
Carrying amount	1,064.5	1,064.5	1,046.5
Customer Relationships
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Gross	2,348.1	2,348.1	2,304.8
Finite-Lived Intangible Assets, Accumulated Amortization	(754.8)	(754.8)	(681.9)
Finite-Lived Intangible Assets, Net	1,593.3	1,593.3	1,622.9
Customer Relationships | Supreme Protein
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Net	7.5	7.5
Trademarks and brands
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Gross	852	852	795
Finite-Lived Intangible Assets, Accumulated Amortization	(295.6)	(295.6)	(266.9)
Finite-Lived Intangible Assets, Net	556.4	556.4	528.1
Trademarks and brands | Supreme Protein
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Net	4.7	4.7
Other Intangible Assets
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Gross	3.1	3.1	3.1
Finite-Lived Intangible Assets, Accumulated Amortization	(3.1)	(3.1)	(3.1)
Finite-Lived Intangible Assets, Net	$ 0	$ 0	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Derivatives, Fair Value
Losses (gains) reclassified to net earnings	$ 0.6	$ (0.2)	$ 1.1	$ 7
Accumulated Other Comprehensive Income, Remaining Net Loss to be Amortized	8.3		8.3		$ 9.4
Assets, Total
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	63.5		63.5		14.7
Liabilities, Total
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	317.9		317.9		543.1
Commodity contracts | Other Current Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	8.2		8.2		5
Commodity contracts | Other Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	6		6		0.1
Commodity contracts | Other Current Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	0.6		0.6		1.4
Commodity contracts | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	36.7		36.7		24.7
Energy Contracts | Other Current Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	5.2		5.2		1.8
Energy Contracts | Other Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	4.1		4.1		0.9
Energy Contracts | Other Current Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	0		0		10.1
Energy Contracts | Other Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	0		0		3.9
Energy Contracts | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	65.9		65.9		87.1
Foreign Exchange Contract - Forward Contracts | Other Current Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	0		0		0.1
Foreign Exchange Contract - Forward Contracts | Other Current Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	1.1		1.1		0
Foreign Exchange Contract - Forward Contracts | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	20.9		20.9		28.9
Interest Rate Swap | Other Current Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	0		0		6.8
Interest Rate Swap | Other Assets
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	40		40		0
Interest Rate Swap | Other Current Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	68.4		68.4		176.4
Interest Rate Swap | Other Liabilities
Derivatives, Fair Value
Derivative Liability, Fair Value, Gross Liability	247.8		247.8		351.3
Interest Rate Swap | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	620.9		620.9		621.7
Interest Rate Swap | Derivatives Not Designated as Hedging Instruments | Interest expense, net
Derivatives, Fair Value
Losses (gains) reclassified to net earnings			7.2
Interest rate swap, rate lock swaps | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	1,609.8		1,609.8		1,666
Interest rate swap, options | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value
Notional Amount of Derivative	$ 433.3		$ 433.3		$ 433.3
Currency Swap | Portion Designated as Hedging Instruments
Derivatives, Fair Value
Derivative, Notional Amount of Terminated Contracts				448.7
Derivative, Cash Received on Hedge		$ 50.3		$ 50.3

Derivative Financial Instrume_4

Derivative Financial Instruments and Hedging (Gain) Loss recognized in Statement of Operations from derivative instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, (Gain) Loss
Loss (Gain) Recognized in OCI including NCI	$ 0	$ (55.8)	$ 0	$ (22.5)
Mark-to-Market (Gain) Loss, net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(185.7)	224.4	(227.3)	163
Net Loss Reclassified from Accumulated OCI including NCI (a)
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	0.6	0	1.1	7.2
Total Net Hedging (Gain) Loss
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(185.1)	224.4	(226.2)	170.2
Cash Settlements Paid (Received), Net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	14.8	0.2	17.5	19.3
Interest expense, net | Mark-to-Market (Gain) Loss, net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(0.1)	(0.2)	(0.1)	(0.2)
Interest expense, net | Net Loss Reclassified from Accumulated OCI including NCI (a)
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	0.6	0	1.1	7.2
Interest expense, net | Total Net Hedging (Gain) Loss
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	0.5	(0.2)	1	7
Interest expense, net | Cash Settlements Paid (Received), Net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	1.2	(0.2)	2.4	(0.2)
Income on swaps, net | Mark-to-Market (Gain) Loss, net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(185.6)	224.6	(227.2)	163.2
Income on swaps, net | Net Loss Reclassified from Accumulated OCI including NCI (a)
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	0	0	0	0
Income on swaps, net | Total Net Hedging (Gain) Loss
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(185.6)	224.6	(227.2)	163.2
Income on swaps, net | Cash Settlements Paid (Received), Net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	13.6	0.4	15.1	19.5
Derivatives Not Designated as Hedging Instruments | Commodity contracts | Cost of Goods Sold
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(2.3)	8	(9.7)	6.1
Derivatives Not Designated as Hedging Instruments | Energy Contracts | Cost of Goods Sold
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(11.3)	26	(19.3)	23.5
Derivatives Not Designated as Hedging Instruments | Foreign Exchange Contract - Forward Contracts | Selling, General and Administrative Expenses
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(0.3)	(0.1)	1.2	(0.1)
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Interest expense, net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	0.5	0	1	0
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Income on swaps, net
Derivative Instruments, (Gain) Loss
(Gain) Loss Recognized in Statement of Operations	(185.6)	224.6	(227.2)	163.2
Hedging Instruments | Interest rate swaps
Derivative Instruments, (Gain) Loss
Loss (Gain) Recognized in OCI including NCI	0	11	0	9.7
Hedging Instruments | Interest rate swaps | Interest expense, net
Derivative Instruments, (Gain) Loss
Loss (Gain) Reclassified from Accumulated OCI including NCI into Earnings (a)	0.6	(0.2)	1.1	7
Hedging Instruments | Currency Swap
Derivative Instruments, (Gain) Loss
Loss (Gain) Recognized in OCI including NCI	0	(66.8)	0	(32.2)
Hedging Instruments | Currency Swap | Income on swaps, net
Derivative Instruments, (Gain) Loss
Loss (Gain) Reclassified from Accumulated OCI including NCI into Earnings (a)	$ 0	$ 0	$ 0	$ 0

Derivative Financial Instrume_5

Derivative Financial Instruments and Hedging Derivatives designated as hedges and pledged collateral (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2021	Sep. 30, 2020
Derivative Instruments, (Gain) Loss
Accumulated Other Comprehensive Income, Cumulative Changes in Net Gain from Hedges, Before Tax			$ 91.3
Cross Currency Swap Settlements and Unrealized Gains Included in AOCI			99.5	$ 99.5
Cross Currency Swap Settlements and Unrealized Gains Recognized in AOCI	$ 61.6	$ 63
Collateral Already Posted			1.8	4.9
Hedging Instruments
Derivative Instruments, (Gain) Loss
Accumulated Other Comprehensive Income, Cumulative Changes in Net Gain from Hedges, Before Tax			91.3	90.2
Accumulated Other Comprehensive Income, Cumulative Changes in Net Gain from Hedges, Effect Net of Tax			68.8	$ 67.9
Interest Rate Swap | Hedging Instruments
Derivative Instruments, (Gain) Loss
Interest Rate Swap Losses to be Reclassified During Next 12 Months			$ 2.3

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Deferred Compensation Investment	$ 14.8	$ 14.8	$ 12.8
Derivative Asset	63.5	63.5	14.7
Equity Securities	46.7	46.7	27.9
Assets, Fair Value Disclosure	125	125	55.4
Deferred Compensation Liabilities	34	34	29.7
Derivative Liability	317.9	317.9	543.1
Other Liabilities, Fair Value Disclosure	351.9	351.9	572.8
(Gain) loss on assets held for sale	0.1	(0.5)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Deferred Compensation Investment	14.8	14.8	12.8
Derivative Asset	0	0	0
Equity Securities	46.7	46.7	27.9
Assets, Fair Value Disclosure	61.5	61.5	40.7
Deferred Compensation Liabilities	0	0	0
Derivative Liability	0	0	0
Other Liabilities, Fair Value Disclosure	0	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Deferred Compensation Investment	0	0	0
Derivative Asset	63.5	63.5	14.7
Equity Securities	0	0	0
Assets, Fair Value Disclosure	63.5	63.5	14.7
Deferred Compensation Liabilities	34	34	29.7
Derivative Liability	317.9	317.9	543.1
Other Liabilities, Fair Value Disclosure	351.9	351.9	572.8
Debt, Fair Value	7,216.5	7,216.5	7,277.8
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets Held for Sale, Fair Value	$ 0	0	$ 7.3
(Gain) loss on assets held for sale		(0.5)
Proceeds from Sale of Assets and Liabilities Held for Sale		(7.9)
Currency translation adjustment		$ 0.1

Commitments and Contingencies_2

Commitments and Contingencies (Details) - Michael Foods $ in Millions	Dec. 31, 2016USD ($)	Mar. 31, 2021USD ($)defendant	Sep. 30, 2020USD ($)
Loss Contingencies
Claims filed, number		22
Loss Contingency, Number of Defendants | defendant		20
Loss Contingency, Pending Claims, Number of Plaintiff Groups		3
Litigation Settlement, Amount Awarded to Other Party	$ 75
Estimated Litigation Liability, Current		$ 3.5	$ 3.5

Leases (Details)

Leases (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	9 years		9 years		7 years
Operating Lease, Weighted Average Discount Rate, Percent	4.63%		4.63%		4.40%
Operating Lease, Right-of-Use Asset	$ 141.1		$ 141.1		$ 116.3
Operating Lease, Liability, Current	25.8		25.8		23.6
Operating Lease, Liability, Noncurrent	130.2		130.2		103
Operating Lease, Liability	156		156		$ 126.6
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	16		16
Lessee, Operating Lease, Liability, Payments, Due Year Two	31.3		31.3
Lessee, Operating Lease, Liability, Payments, Due Year Three	27.8		27.8
Lessee, Operating Lease, Liability, Payments, Due Year Four	21		21
Lessee, Operating Lease, Liability, Payments, Due Year Five	14.9		14.9
Lessee, Operating Lease, Liability, Payments, Due after Year Five	79.6		79.6
Lessee, Operating Lease, Liability, Payments, Due	190.6		190.6
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	34.6		34.6
Operating Lease, Cost	11	$ 10.1	21.4	$ 21.1
Variable Lease, Cost	1.2	1.3	2.7	2.5
Short-term Lease, Cost	2	$ 1.7	3.6	3.7
Operating Lease, Payments			15.3	14.5
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			36.6	$ 0.8
Almark Foods
Lessee, Lease, Description [Line Items]
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			32.9
Other assets	$ 32.9		$ 32.9
Minimum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	56 years		56 years

Long-Term Debt (Details)

Long-Term Debt (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Feb. 26, 2021	Sep. 30, 2020USD ($)
Debt Instrument
Long-term Debt, Including Current Maturities	$ 7,075,100,000		$ 7,075,100,000			$ 7,049,700,000
Current portion of long-term debt	74,300,000		74,300,000			64,900,000
Debt Issuance Costs, net	55,700,000		55,700,000			62,600,000
Plus: Unamortized premium and discount, net	35,900,000		35,900,000			36,800,000
Total Long-term Debt	6,981,000,000		6,981,000,000			6,959,000,000
Repayments of Long-term Debt			1,794,600,000	$ 3,731,500,000
Payments of Debt Issuance Costs			16,800,000	39,800,000
Gross Repayments of Long-term debt	$ 1,757,100,000	$ 1,157,000,000	1,794,600,000	3,731,500,000
Payments of debt premiums and refinancing fees			$ 75,800,000	49,800,000
Debt Covenant, Leverage Ratio	4.25		4.25
Debt Covenant, Percentage of Revolving Credit Commitments	30.00%		30.00%
Term Loan
Debt Instrument
Gross Repayments of Long-term debt				1,309,500,000
Revolving Credit Facility
Debt Instrument
Line of Credit Facility, Current Borrowing Capacity	$ 750,000,000		$ 750,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
Letters of Credit Outstanding, Amount	19,300,000		$ 19,300,000
Line of Credit Facility, Remaining Borrowing Capacity	730,700,000		730,700,000
Debt Covenant, Maximum Undischarged Judgments	100,000,000		$ 100,000,000
Revolving Credit Facility | Minimum
Debt Instrument
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
Revolving Credit Facility | Maximum
Debt Instrument
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.375%
Revolving Credit Facility | Base Rate
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.50%
Revolving Credit Facility | Base Rate | Minimum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.50%
Revolving Credit Facility | Base Rate | Maximum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.00%
Revolving Credit Facility | Base Rate | Median
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.75%
Revolving Credit Facility | Federal Funds
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.50%
Revolving Credit Facility | One-Month Eurodollar
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.00%
Revolving Credit Facility | Eurodollar
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.50%
Revolving Credit Facility | Eurodollar | Minimum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.50%
Revolving Credit Facility | Eurodollar | Maximum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			2.00%
Revolving Credit Facility | Eurodollar | Median
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.75%
Line of Credit
Debt Instrument
Line of Credit Facility, Current Borrowing Capacity	75,000,000		$ 75,000,000
Bridge Loan
Debt Instrument
Gross Repayments of Long-term debt				1,225,000,000
BellRing Term B Facility
Debt Instrument
Long-term Debt	627,400,000		$ 627,400,000			673,700,000
BellRing Term B Facility | Base Rate
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			3.00%
BellRing Revolving Credit Facility
Debt Instrument
Long-term Debt	0		$ 0			30,000,000
Municipal Bonds
Debt Instrument
Long-term Debt	7,500,000		7,500,000			8,500,000
Gross Repayments of Long-term debt	1,000,000	1,100,000	1,000,000	1,100,000
Credit Agreement
Debt Instrument
Gross Repayments of Long-term debt		0		0
4.50% Senior Notes Maturing in September 2031 | Senior Notes
Debt Instrument
Long-term Debt	1,800,000,000		1,800,000,000			0
Proceeds from Issuance of Debt			1,783,200,000
Payments of Debt Issuance Costs			16,800,000
4.625% Senior Notes Maturing April 2030 | Senior Notes
Debt Instrument
Long-term Debt	1,650,000,000		1,650,000,000			1,650,000,000
5.50% Senior Notes Maturing in December 2029 | Senior Notes
Debt Instrument
Long-term Debt	750,000,000		750,000,000			750,000,000
5.625% Senior Notes maturing January 2028 | Senior Notes
Debt Instrument
Long-term Debt	940,900,000		940,900,000			940,900,000
5.75% Senior Notes Maturing March 2027 | Senior Notes
Debt Instrument
Long-term Debt	1,299,300,000		1,299,300,000			1,299,300,000
5.00% Senior Notes maturing August 2026 | Senior Notes
Debt Instrument
Long-term Debt	0		0			$ 1,697,300,000
Gross Repayments of Long-term debt	1,697,300,000		1,697,300,000
8.00% Senior Notes maturing July 2025 | Senior Notes
Debt Instrument
Gross Repayments of Long-term debt		122,200,000		122,200,000
5.50% Senior Notes Maturing March 2025 | Senior Notes
Debt Instrument
Gross Repayments of Long-term debt		1,000,000,000		1,000,000,000
(Gain) loss on extinguishment of debt and refinancing fees, net
Debt Instrument
Payments of debt premiums and refinancing fees	75,800,000	49,800,000	75,800,000	49,800,000
Write off of Debt Issuance Costs and Deferred Financing Fees	18,900,000	10,200,000	18,900,000	23,100,000
(Gain) loss on extinguishment of debt and refinancing fees, net | Term Loan
Debt Instrument
Payments of debt premiums and refinancing fees				0
Write off of Debt Issuance Costs and Deferred Financing Fees				9,100,000
(Gain) loss on extinguishment of debt and refinancing fees, net | Bridge Loan
Debt Instrument
Payments of debt premiums and refinancing fees				0
Write off of Debt Issuance Costs and Deferred Financing Fees				3,800,000
(Gain) loss on extinguishment of debt and refinancing fees, net | Municipal Bonds
Debt Instrument
Payments of debt premiums and refinancing fees	0	0	0	0
Write off of Debt Issuance Costs and Deferred Financing Fees	0	0	0	0
(Gain) loss on extinguishment of debt and refinancing fees, net | Credit Agreement
Debt Instrument
Payments of debt premiums and refinancing fees		0		0
Write off of Debt Issuance Costs and Deferred Financing Fees		800,000		800,000
(Gain) loss on extinguishment of debt and refinancing fees, net | 5.00% Senior Notes maturing August 2026 | Senior Notes
Debt Instrument
Payments of debt premiums and refinancing fees	74,300,000		74,300,000
Write off of Debt Issuance Costs and Deferred Financing Fees	18,900,000		18,900,000
(Gain) loss on extinguishment of debt and refinancing fees, net | 8.00% Senior Notes maturing July 2025 | Senior Notes
Debt Instrument
Payments of debt premiums and refinancing fees		8,500,000		8,500,000
Write off of Debt Issuance Costs and Deferred Financing Fees		700,000		700,000
(Gain) loss on extinguishment of debt and refinancing fees, net | 5.50% Senior Notes Maturing March 2025 | Senior Notes
Debt Instrument
Payments of debt premiums and refinancing fees		41,300,000		41,300,000
Write off of Debt Issuance Costs and Deferred Financing Fees		8,700,000		8,700,000
BellRing | BellRing Term B Facility
Debt Instrument
Debt Instrument, Periodic Payment, Principal			$ 8,750,000
Reduction in interest rate margin, basis points					100
Premium on early repayment of debt			1.00%
Loans Payable to Bank	700,000,000		$ 700,000,000
Excess cash flow prepayment			28,800,000
Excess cash flow prepayment, current maturities of debt	$ 38,200,000		$ 38,200,000
Debt Instrument, Interest Rate, Effective Percentage	4.75%		4.75%			6.00%
Gross Repayments of Long-term debt	$ 8,800,000	8,700,000	$ 46,300,000	8,700,000
BellRing | BellRing Term B Facility | Federal Funds
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.50%
BellRing | BellRing Term B Facility | One-Month Eurodollar
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			1.00%
BellRing | BellRing Term B Facility | One-Month Eurodollar | Minimum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			0.75%
BellRing | BellRing Term B Facility | Eurodollar
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			4.00%
BellRing | BellRing Revolving Credit Facility
Debt Instrument
Line of Credit Facility, Current Borrowing Capacity	200,000,000		$ 200,000,000
Line of Credit Facility, Maximum Borrowing Capacity	20,000,000		$ 20,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.50%
Letters of Credit Outstanding, Amount	0		$ 0			$ 0
Line of Credit Facility, Remaining Borrowing Capacity	200,000,000		200,000,000			$ 170,000,000
Debt Covenant, Maximum Undischarged Judgments	65,000,000		65,000,000
Proceeds from Lines of Credit			20,000,000	185,000,000
Debt Instrument, Interest Rate, Effective Percentage						5.25%
Gross Repayments of Long-term debt	50,000,000	25,000,000	$ 50,000,000	65,000,000
BellRing | BellRing Revolving Credit Facility | Minimum
Debt Instrument
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
BellRing | BellRing Revolving Credit Facility | Maximum
Debt Instrument
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.50%
BellRing | BellRing Revolving Credit Facility | Base Rate
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			3.25%
BellRing | BellRing Revolving Credit Facility | Base Rate | Minimum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			2.75%
BellRing | BellRing Revolving Credit Facility | Base Rate | Maximum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			3.25%
BellRing | BellRing Revolving Credit Facility | Base Rate | Median
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			3.00%
BellRing | BellRing Revolving Credit Facility | Eurodollar
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			4.25%
BellRing | BellRing Revolving Credit Facility | Eurodollar | Minimum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			3.75%
BellRing | BellRing Revolving Credit Facility | Eurodollar | Maximum
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			4.25%
BellRing | BellRing Revolving Credit Facility | Eurodollar | Median
Debt Instrument
Debt Instrument, Basis Spread on Variable Rate			4.00%
BellRing | BellRing Credit Agreement
Debt Instrument
Gross Repayments of Long-term debt	$ 0		$ 0
Debt Covenant, Leverage Ratio	6		6
BellRing | (Gain) loss on extinguishment of debt and refinancing fees, net | BellRing Term B Facility
Debt Instrument
Payments of debt premiums and refinancing fees	$ 0	0	$ 0	0
Write off of Debt Issuance Costs and Deferred Financing Fees	0	0	0	0
BellRing | (Gain) loss on extinguishment of debt and refinancing fees, net | BellRing Revolving Credit Facility
Debt Instrument
Payments of debt premiums and refinancing fees	0	0	0	0
Write off of Debt Issuance Costs and Deferred Financing Fees	0	$ 0	0	$ 0
BellRing | (Gain) loss on extinguishment of debt and refinancing fees, net | BellRing Credit Agreement
Debt Instrument
Payments of debt premiums and refinancing fees	1,500,000		1,500,000
Write off of Debt Issuance Costs and Deferred Financing Fees	$ 0		$ 0
Less than or equal to 3.35 | BellRing | BellRing Revolving Credit Facility
Debt Instrument
Debt Covenant, Leverage Ratio	3.35		3.35
High-End Ratio | Revolving Credit Facility
Debt Instrument
Debt Covenant, Leverage Ratio	3		3
High-End Ratio | BellRing | BellRing Revolving Credit Facility
Debt Instrument
Debt Covenant, Leverage Ratio	3.50		3.50
Low-End Ratio | Revolving Credit Facility
Debt Instrument
Debt Covenant, Leverage Ratio	1.50		1.50
Low-End Ratio | BellRing | BellRing Revolving Credit Facility
Debt Instrument
Debt Covenant, Leverage Ratio	2.50		2.50

Pension and Other Postretirem_3

Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Gain) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits | North America
Components of net periodic benefit cost (gain)
Service cost	$ 1	$ 1	$ 1.9	$ 2.1
Interest cost	0.8	0.9	1.6	1.8
Expected return on plan assets	(1.6)	(1.6)	(3.2)	(3.2)
Recognized net actuarial loss	0.6	0.4	1.2	0.9
Recognized prior service cost (credit)	0	0.1	0	0.1
Net periodic benefit cost (gain)	0.8	0.8	1.5	1.7
Pension Benefits | Other International
Components of net periodic benefit cost (gain)
Interest cost	3.8	3.7	7.5	7.4
Expected return on plan assets	(6.3)	(6.2)	(12.3)	(12.4)
Recognized prior service cost (credit)	0.1	0	0.2	0
Net periodic benefit cost (gain)	(2.4)	(2.5)	(4.6)	(5)
Other Postretirement Benefit Plan | North America
Components of net periodic benefit cost (gain)
Service cost	0.1	0.2	0.2	0.3
Interest cost	0.4	0.4	0.8	0.9
Recognized net actuarial loss	0.3	0.1	0.6	0.3
Recognized prior service cost (credit)	(1.2)	(1.1)	(2.4)	(2.3)
Net periodic benefit cost (gain)	$ (0.4)	$ (0.4)	$ (0.8)	$ (0.8)

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Equity, Class of Treasury Stock [Line Items]
Total Share Repurchase Cost			$ 322.7	$ 437.8
Payments for share repurchase contracts					$ 46.4
Cash received from share repurchase contracts			47.5	0
Common Stock
Equity, Class of Treasury Stock [Line Items]
Payments for accrued repurchases of common stock			$ 7.4	$ 8.7
Common Stock
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	1.6	2	3.3	4.2
Average price per share	$ 98.29	$ 101.77	$ 95.78	$ 102.40
Total Share Repurchase Cost	$ 155.4	$ 206	$ 315.3	$ 429.1

Segments (Details)

Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Segment Reporting Information
Net Sales	$ 1,483.3	$ 1,494.2	$ 2,941.3	$ 2,951
Interest expense, net	94.8	94	191.4	196.9
Loss on extinguishment and refinancing of debt, net	94.7	60	94.7	72.9
(Income) expense on swaps, net	(185.6)	224.6	(227.2)	163.2
Earnings (loss) before income taxes and equity method loss	147.3	(221.8)	269.4	(77)
Depreciation and amortization	113.4	91.5	207.5	181.8
Assets	12,141		12,141		$ 12,146.7
Corporate
Segment Reporting Information
General corporate expenses and other	15.1	52.7	28.9	80.1
Depreciation and amortization	1	1.1	2	2
Assets	1,013.7		1,013.7		1,315
Operating Segments
Segment Reporting Information
Net Sales	1,483.3	1,494.2	2,941.3	2,951
Segment Profit (Loss)	166.3	209.5	357.2	436.1
Depreciation and amortization	112.4	90.4	205.5	179.8
Operating Segments | Post Consumer Brands
Segment Reporting Information
Net Sales	479.9	507.9	924.9	949.1
Segment Profit (Loss)	91.8	92.4	162.3	173
Depreciation and amortization	29.2	28.1	57.4	56
Assets	3,407.9		3,407.9		3,291.7
Operating Segments | Weetabix
Segment Reporting Information
Net Sales	113.4	113.4	226.9	214.9
Segment Profit (Loss)	25.9	28	54	51.7
Depreciation and amortization	9.4	8.6	18.8	17.3
Assets	1,983.3		1,983.3		1,864.5
Operating Segments | Foodservice
Segment Reporting Information
Net Sales	369.2	378.4	723.7	799
Segment Profit (Loss)	8.8	23.8	19.6	70.8
Depreciation and amortization	31.6	29.7	62.3	58.7
Operating Segments | Refrigerated Retail
Segment Reporting Information
Net Sales	239.5	237.6	502.6	487.5
Segment Profit (Loss)	24.2	30.2	57.9	56.2
Depreciation and amortization	18.3	17.6	36.4	35
Operating Segments | Foodservice and Refrigerated Retail
Segment Reporting Information
Assets	5,096.9		5,096.9		5,022
Operating Segments | BellRing Brands
Segment Reporting Information
Net Sales	282.1	257.5	564.5	501.5
Segment Profit (Loss)	15.6	35.1	63.4	84.4
Depreciation and amortization	23.9	6.4	30.6	12.8
Assets	639.2		639.2		$ 653.5
Eliminations | Segment Eliminations
Segment Reporting Information
Net Sales	(0.8)	(0.6)	(1.3)	(1)
Cereal and granola | Operating Segments
Segment Reporting Information
Net Sales	575.7	621.1	1,134	1,163.6
Nut butters | Operating Segments
Segment Reporting Information
Net Sales	17.4	0	17.4	0
Eggs and egg products | Operating Segments
Segment Reporting Information
Net Sales	353.8	363.2	691.9	758.5
Side dishes (including potato products) | Operating Segments
Segment Reporting Information
Net Sales	138.4	143.1	293.9	291.6
Cheese and dairy | Operating Segments
Segment Reporting Information
Net Sales	54.6	56.5	117.3	124.1
Sausage | Operating Segments
Segment Reporting Information
Net Sales	43	40.3	87.3	86.2
Protein-based products and supplements | Operating Segments
Segment Reporting Information
Net Sales	282.2	257.6	564.7	501.7
Other | Operating Segments
Segment Reporting Information
Net Sales	18.8	12.9	35.8	26.1
Product Eliminations | Eliminations
Segment Reporting Information
Net Sales	$ (0.6)	$ (0.5)	$ (1)	$ (0.8)