Condensed Financial Statements Of Guarantors (Condensed Consolidating Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2011	Sep. 30, 2010
Assets
Cash and cash equivalents	$ 131.4	$ 50.0	$ 41.4	$ 29.3
Marketable securities	0.8	8.2
Investment in Post Holdings, Inc.	223.1
Receivables, net	345.1	349.6
Inventories	448.6	424.1
Deferred income taxes	14.2	15.7
Prepaid expenses and other current assets	19.2	11.8
Current assets of Discontinued Operations		135.3
Total Current Assets	1,182.4	994.7
Property	1,539.6	1,424.3
Accumulated Depreciation	(692.2)	(641.1)
Goodwill	1,391.4	1,160.9
Other Intangible Assets	1,244.2	987.7
Accumulated Amortization	(252.2)	(219.8)
Other Assets	39.5	35.8
Noncurrent Assets of Discontinued Operations		2,536.7
Total Assets	4,452.7	6,279.2
Liabilities and Shareholders' Equity
Accounts payable	244.1	284.4
Notes payable to banks		105.0
Current portion of long-term debt	85.7	30.7
Other current liabilities	160.9	192.1
Current liabilities of Discontinued Operations		59.7
Total Current Liabilities	490.7	671.9
Long-term Debt	1,895.5	2,172.5
Deferred Income Taxes	269.7	281.0
Other Liabilities	117.5	129.1
Noncurrent Liabilities of Discontinued Operations		459.5
Total Liabilities	2,773.4	3,714.0
Shareholders' Equity
Common stock	0.6	0.6
Other shareholders' equity	1,678.7	2,564.6
Total Shareholders' Equity	1,679.3	2,565.2
Total Liabilities and Shareholders' Equity	4,452.7	6,279.2
Parent Company [Member]
Assets
Cash and cash equivalents	69.3	2.5	0.4	0.6
Marketable securities	0.8	8.2
Investment in Post Holdings, Inc.	223.1
Receivables, net	56.3	55.7
Inventories	72.4	65.2
Deferred income taxes	14.4	14.4
Prepaid expenses and other current assets	8.7	3.4
Total Current Assets	445.0	149.4
Investment in Subsidiaries	3,350.4	4,873.5
Deferred Income Taxes	46.5	46.5
Property	255.4	252.5
Accumulated Depreciation	(179.7)	(177.1)
Other Intangible Assets	52.7	66.3
Accumulated Amortization	(34.0)	(40.8)
Other Assets	38.4	34.5
Noncurrent Assets of Discontinued Operations		39.7
Total Assets	3,974.7	5,244.5
Liabilities and Shareholders' Equity
Accounts payable	77.1	74.7
Current portion of long-term debt	85.7	30.7
Other current liabilities	82.7	112.0
Current liabilities of Discontinued Operations		4.1
Total Current Liabilities	245.5	221.5
Intercompany Notes and Interest	76.9	91.7
Long-term Debt	1,895.5	2,172.5
Other Liabilities	77.5	97.6
Noncurrent Liabilities of Discontinued Operations		96.0
Total Liabilities	2,295.4	2,679.3
Shareholders' Equity
Common stock	0.6	0.6
Other shareholders' equity	1,678.7	2,564.6
Total Shareholders' Equity	1,679.3	2,565.2
Total Liabilities and Shareholders' Equity	3,974.7	5,244.5
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents			0.8	0.3
Receivables, net	69.4	65.9
Inventories	352.7	334.9
Deferred income taxes		1.1
Prepaid expenses and other current assets	9.1	7.1
Total Current Assets	431.2	409.0
Intercompany Notes and Interest	41.0	88.8
Investment in Subsidiaries	309.8	271.4
Property	1,114.2	1,015.9
Accumulated Depreciation	(466.3)	(426.8)
Goodwill	1,286.6	1,068.1
Other Intangible Assets	1,112.7	850.7
Accumulated Amortization	(198.3)	(163.3)
Other Assets	0.9	1.1
Total Assets	3,631.8	3,114.9
Liabilities and Shareholders' Equity
Accounts payable	145.6	180.7
Deferred income taxes	0.4
Other current liabilities	69.3	67.6
Total Current Liabilities	215.3	248.3
Intercompany Notes and Interest	15.1	15.1
Deferred Income Taxes	314.1	325.4
Other Liabilities	5.7	2.4
Total Liabilities	550.2	591.2
Shareholders' Equity
Other shareholders' equity	3,081.6	2,523.7
Total Shareholders' Equity	3,081.6	2,523.7
Total Liabilities and Shareholders' Equity	3,631.8	3,114.9
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	67.1	50.8	40.2	28.4
Receivables, net	222.6	233.5
Inventories	23.5	24.0
Deferred income taxes	0.2	0.2
Prepaid expenses and other current assets	1.4	1.3
Current assets of Discontinued Operations		135.3
Total Current Assets	314.8	445.1
Intercompany Notes and Interest	92.0	106.8
Property	170.0	155.9
Accumulated Depreciation	(46.2)	(37.2)
Goodwill	104.8	92.8
Other Intangible Assets	78.8	70.7
Accumulated Amortization	(19.9)	(15.7)
Other Assets	0.2	0.2
Noncurrent Assets of Discontinued Operations		2,535.9
Total Assets	694.5	3,354.5
Liabilities and Shareholders' Equity
Accounts payable	29.6	37.8
Notes payable to banks		105.0
Other current liabilities	8.9	12.5
Current liabilities of Discontinued Operations		55.6
Total Current Liabilities	38.5	210.9
Intercompany Notes and Interest	41.0	88.8
Deferred Income Taxes	2.1	2.1
Other Liabilities	34.3	29.1
Noncurrent Liabilities of Discontinued Operations		402.4
Total Liabilities	115.9	733.3
Shareholders' Equity
Other shareholders' equity	578.6	2,621.2
Total Shareholders' Equity	578.6	2,621.2
Total Liabilities and Shareholders' Equity	694.5	3,354.5
Eliminations [Member]
Assets
Cash and cash equivalents	(5.0)	(3.3)
Receivables, net	(3.2)	(5.5)
Deferred income taxes	(0.4)
Total Current Assets	(8.6)	(8.8)
Intercompany Notes and Interest	(133.0)	(195.6)
Investment in Subsidiaries	(3,660.2)	(5,144.9)
Deferred Income Taxes	(46.5)	(46.5)
Noncurrent Assets of Discontinued Operations		(38.9)
Total Assets	(3,848.3)	(5,434.7)
Liabilities and Shareholders' Equity
Accounts payable	(8.2)	(8.8)
Deferred income taxes	(0.4)
Total Current Liabilities	(8.6)	(8.8)
Intercompany Notes and Interest	(133.0)	(195.6)
Deferred Income Taxes	(46.5)	(46.5)
Noncurrent Liabilities of Discontinued Operations		(38.9)
Total Liabilities	(188.1)	(289.8)
Shareholders' Equity
Other shareholders' equity	(3,660.2)	(5,144.9)
Total Shareholders' Equity	(3,660.2)	(5,144.9)
Total Liabilities and Shareholders' Equity	$ (3,848.3)	$ (5,434.7)