Condensed Financial Statements Of Guarantors (Condensed Consolidating Balance Sheets) (Details) (USD $) In Millions	Jun. 30, 2011	Sep. 30, 2010	Jun. 30, 2010	Sep. 30, 2009
Assets
Cash and cash equivalents	$ 47.2	$ 29.3	$ 115.3	$ 282.8
Marketable securities	10.7	10.0
Investment in Ralcorp Receivables Corporation		137.8
Receivables, net	344.7	233.4
Inventories	468.5	425.1
Deferred income taxes	10.7	10.6
Prepaid expenses and other current assets	19.2	30.8
Total Current Assets	901.0	877.0
Property	1,948.5	1,858.5
Accumulated depreciation	(746.6)	(639.5)
Goodwill	2,952.0	2,945.7
Other Intangible Assets	1,884.7	1,908.8
Accumulated amortization	(241.1)	(181.8)
Other Assets	39.6	36.2
Total Assets	6,738.1	6,804.9
Liabilities and Shareholders' Equity
Accounts and notes payable	427.8	279.5
Other current liabilities	217.0	347.6
Total Current Liabilities	644.8	627.1
Long-term Debt	2,162.5	2,464.9
Deferred Income Taxes	636.4	685.1
Other Liabilities	235.5	198.6
Total Liabilities	3,679.2	3,975.7
Shareholders' Equity
Common stock	0.6	0.6
Other shareholders' equity	3,058.3	2,828.6
Total Shareholders' Equity	3,058.9	2,829.2
Total Liabilities and Shareholders' Equity	6,738.1	6,804.9
Parent Company [Member]
Assets
Cash and cash equivalents	1.0	0.6	97.4	263.5
Marketable securities	10.7	10.0
Investment in Ralcorp Receivables Corporation		180.0
Receivables, net	48.3	18.2
Inventories	61.6	67.6
Deferred income taxes		2.1
Prepaid expenses and other current assets	7.9	17.4
Total Current Assets	129.5	295.9
Investment in Subsidiaries	5,528.5	5,339.1
Deferred Income Taxes	5.5	81.0
Property	247.8	243.0
Accumulated depreciation	(174.8)	(165.7)
Other Intangible Assets	62.4	57.5
Accumulated amortization	(39.0)	(34.9)
Other Assets	12.1	35.1
Total Assets	5,772.0	5,851.0
Liabilities and Shareholders' Equity
Accounts and notes payable	103.8	64.3
Deferred Income Taxes	8.9
Other current liabilities	111.2	248.9
Total Current Liabilities	223.9	313.2
Intercompany Notes and Interest	137.3	83.0
Long-term Debt	2,162.4	2,464.9
Other Liabilities	189.5	160.7
Total Liabilities	2,713.1	3,021.8
Shareholders' Equity
Common stock	0.6	0.6
Other shareholders' equity	3,058.3	2,828.6
Total Shareholders' Equity	3,058.9	2,829.2
Total Liabilities and Shareholders' Equity	5,772.0	5,851.0
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		0.3		0.2
Receivables, net	47.0	182.0
Inventories	376.0	329.3
Deferred income taxes	20.2	9.1
Prepaid expenses and other current assets	8.9	10.0
Total Current Assets	452.1	530.7
Intercompany Notes and Interest	20.8	20.8
Investment in Subsidiaries	382.8	347.2
Property	1,457.8	1,389.3
Accumulated depreciation	(517.1)	(436.8)
Goodwill	2,844.3	2,844.7
Other Intangible Assets	1,745.6	1,779.3
Accumulated amortization	(186.4)	(136.6)
Other Assets	27.3	1.0
Total Assets	6,227.2	6,339.6
Liabilities and Shareholders' Equity
Accounts and notes payable	165.0	178.6
Other current liabilities	82.8	84.5
Total Current Liabilities	247.8	263.1
Intercompany Notes and Interest	15.1	15.1
Long-term Debt	0.1
Deferred Income Taxes	644.3	753.2
Other Liabilities	10.7	7.8
Total Liabilities	918.0	1,039.2
Shareholders' Equity
Other shareholders' equity	5,309.3	5,300.4
Total Shareholders' Equity	5,309.3	5,300.4
Total Liabilities and Shareholders' Equity	6,227.3	6,339.6
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	47.4	28.4	17.9	19.1
Receivables, net	250.8	173.8
Inventories	30.9	28.2
Deferred income taxes		(0.6)
Prepaid expenses and other current assets	2.4	3.4
Total Current Assets	331.5	233.2
Intercompany Notes and Interest	152.4	98.1
Deferred Income Taxes	2.4
Property	242.9	226.2
Accumulated depreciation	(54.7)	(37.0)
Goodwill	107.7	101.0
Other Intangible Assets	76.7	72.0
Accumulated amortization	(15.7)	(10.3)
Other Assets	0.2	0.1
Total Assets	843.4	683.3
Liabilities and Shareholders' Equity
Accounts and notes payable	161.6	39.4
Deferred Income Taxes	0.6
Other current liabilities	23.0	14.2
Total Current Liabilities	185.2	53.6
Intercompany Notes and Interest	20.8	20.8
Deferred Income Taxes		12.9
Other Liabilities	35.3	30.1
Total Liabilities	241.3	117.4
Shareholders' Equity
Other shareholders' equity	602.1	565.9
Total Shareholders' Equity	602.1	565.9
Total Liabilities and Shareholders' Equity	843.4	683.3
Eliminations [Member]
Assets
Cash and cash equivalents	(1.2)
Investment in Ralcorp Receivables Corporation		(42.2)
Receivables, net	(1.4)	(140.6)
Deferred income taxes	(9.5)
Total Current Assets	(12.1)	(182.8)
Intercompany Notes and Interest	(173.2)	(118.9)
Investment in Subsidiaries	(5,911.3)	(5,686.3)
Deferred Income Taxes	(7.9)	(81.0)
Total Assets	(6,104.5)	(6,069.0)
Liabilities and Shareholders' Equity
Accounts and notes payable	(2.6)	(2.8)
Deferred Income Taxes	(9.5)
Total Current Liabilities	(12.1)	(2.8)
Intercompany Notes and Interest	(173.2)	(118.9)
Deferred Income Taxes	(7.9)	(81.0)
Total Liabilities	(193.2)	(202.7)
Shareholders' Equity
Other shareholders' equity	(5,911.3)	(5,866.3)
Total Shareholders' Equity	(5,911.3)	(5,866.3)
Total Liabilities and Shareholders' Equity	$ (6,104.5)	$ (6,069.0)