Condensed Financial Statements Of Guarantors (Condensed Consolidating Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2008
Assets
Cash and cash equivalents	$ 50.0	$ 29.3	$ 282.8	$ 14.1
Marketable securities	8.2	10.0
Investment in Ralcorp Receivables Corporation	0	137.8	134.4
Receivables, net	410.4	233.4
Inventories	490.7	425.1
Deferred income taxes	19.6	10.6
Prepaid expenses and other current assets	15.8	30.8
Total Current Assets	994.7	877.0
Property	1,969.4	1,858.5
Accumulated Depreciation	(774.1)	(639.5)
Goodwill	2,590.1	2,945.7	2,386.6
Other Intangible Assets	1,776.2	1,908.8
Accumulated Amortization	(259.7)	(181.8)
Other Assets	36.6	36.2
Total Assets	6,333.2	6,804.9	5,452.2
Liabilities and Shareholders' Equity
Accounts and notes payable	418.2	279.5
Other current liabilities	253.7	347.6
Total Current Liabilities	671.9	627.1
Long-term Debt	2,172.5	2,464.9
Deferred Income Taxes	635.6	685.1
Other Liabilities	234.0	198.6
Total Liabilities	3,714.0	3,975.7
Shareholders' Equity
Common stock, par value $.01 per share	0.6	0.6
Other shareholders' equity	2,618.6	2,828.6
Total Shareholders' Equity	2,619.2	2,829.2	2,705.6	2,411.5
Total Liabilities and Shareholders' Equity	6,333.2	6,804.9
Parent Company [Member]
Assets
Cash and cash equivalents	2.5	0.6	263.5	6.0
Marketable securities	8.2	10.0
Investment in Ralcorp Receivables Corporation		180.0
Receivables, net	57.5	18.2
Inventories	65.2	67.6
Deferred income taxes	14.4	2.1
Prepaid expenses and other current assets	3.4	17.4
Total Current Assets	151.2	295.9
Investment in Subsidiaries	4,921.9	5,342.7
Property	252.5	239.4
Accumulated Depreciation	(177.1)	(165.7)
Other Intangible Assets	66.3	57.5
Accumulated Amortization	(40.8)	(34.9)
Other Assets	11.5	35.1
Total Assets	5,185.5	5,770.0
Liabilities and Shareholders' Equity
Accounts and notes payable	74.7	64.3
Other current liabilities	150.9	248.9
Total Current Liabilities	225.6	313.2
Intercompany Notes and Interest	115.6	83.0
Long-term Debt	2,172.5	2,464.9
Deferred Income Taxes	(141.0)	(81.0)
Other Liabilities	193.6	160.7
Total Liabilities	2,566.3	2,940.8
Shareholders' Equity
Common stock, par value $.01 per share	0.6	0.6
Other shareholders' equity	2,618.6	2,828.6
Total Shareholders' Equity	2,619.2	2,829.2
Total Liabilities and Shareholders' Equity	5,185.5	5,770.0
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		0.3	0.2	0.9
Receivables, net	70.0	182.0
Inventories	395.3	329.3
Deferred income taxes	4.8	9.1
Prepaid expenses and other current assets	10.3	10.0
Total Current Assets	480.4	530.7
Intercompany Notes and Interest	88.8	20.8
Investment in Subsidiaries	267.7	347.2
Property	1,488.8	1,392.9
Accumulated Depreciation	(541.9)	(436.8)
Goodwill	2,491.0	2,844.7
Other Intangible Assets	1,639.2	1,779.3
Accumulated Amortization	(203.2)	(136.6)
Other Assets	24.9	1.0
Total Assets	5,735.7	6,343.2
Liabilities and Shareholders' Equity
Accounts and notes payable	201.8	178.6
Other current liabilities	84.5	84.5
Total Current Liabilities	286.3	263.1
Intercompany Notes and Interest	15.1	15.1
Deferred Income Taxes	765.5	753.2
Other Liabilities	3.2	7.8
Total Liabilities	1,070.1	1,039.2
Shareholders' Equity
Other shareholders' equity	4,665.6	5,304.0
Total Shareholders' Equity	4,665.6	5,304.0
Total Liabilities and Shareholders' Equity	5,735.7	6,343.2
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	50.8	28.4	19.1	7.2
Receivables, net	284.7	173.8
Inventories	30.2	28.2
Deferred income taxes	0.4	(0.6)
Prepaid expenses and other current assets	2.1	3.4
Total Current Assets	368.2	233.2
Intercompany Notes and Interest	130.7	98.1
Property	228.1	226.2
Accumulated Depreciation	(55.1)	(37.0)
Goodwill	99.1	101.0
Other Intangible Assets	70.7	72.0
Accumulated Amortization	(15.7)	(10.3)
Other Assets	0.2	0.1
Total Assets	826.2	683.3
Liabilities and Shareholders' Equity
Accounts and notes payable	146.8	39.4
Other current liabilities	18.3	14.2
Total Current Liabilities	165.1	53.6
Intercompany Notes and Interest	88.8	20.8
Deferred Income Taxes	11.1	12.9
Other Liabilities	37.2	30.1
Total Liabilities	302.2	117.4
Shareholders' Equity
Other shareholders' equity	524.0	565.9
Total Shareholders' Equity	524.0	565.9
Total Liabilities and Shareholders' Equity	826.2	683.3
Eliminations [Member]
Assets
Cash and cash equivalents	(3.3)
Investment in Ralcorp Receivables Corporation		(42.2)
Receivables, net	(1.8)	(140.6)
Total Current Assets	(5.1)	(182.8)
Intercompany Notes and Interest	(219.5)	(118.9)
Investment in Subsidiaries	(5,189.6)	(5,689.9)
Total Assets	(5,414.2)	(5,991.6)
Liabilities and Shareholders' Equity
Accounts and notes payable	(5.1)	(2.8)
Total Current Liabilities	(5.1)	(2.8)
Intercompany Notes and Interest	(219.5)	(118.9)
Total Liabilities	(224.6)	(121.7)
Shareholders' Equity
Other shareholders' equity	(5,189.6)	(5,869.9)
Total Shareholders' Equity	(5,189.6)	(5,869.9)
Total Liabilities and Shareholders' Equity	$ (5,414.2)	$ (5,991.6)