Business Combinations (Provisional Purchase Price Allocation And Adjustment During The Period) (Details) (USD $) In Millions	9 Months Ended				9 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Sep. 30, 2010 Acquisition Date Amounts [Member]		Jun. 30, 2011 Adjustments During Period [Member]		Jun. 30, 2011 Acquisition Date Amounts As Adjusted [Member]		Jun. 30, 2011 Sepps Gourmet Foods Ltd [Member]	Jun. 30, 2011 American Italian Pasta Company [Member]
Cash			$ 41.1	[1]			$ 41.1
Cash	17.9	(167.5)
Receivables			53.7	[1],[2]			54.4	[2]
Receivables					0.7	[2]
Inventories			55.6	[1],[3]			55.4	[3]
Inventories					(0.2)	[3]
Other current assets			22.2	[1],[2]			22.0	[2]
Other current assets					(0.2)	[2]
Property			306.1	[1],[4]			307.7	[4]	0.1	1.5
Property					1.6	[4]
Goodwill			577.4	[1]			577.1
Goodwill					(0.3)
Other intangible assets			612.9	[1],[3]			610.9	[3]
Other intangible assets					(2.0)	[3]
Other assets			0.6	[1],[2]			1.1	[2]
Other assets					0.5	[2]
Total assets acquired			1,669.6	[1]			1,669.7
Total assets acquired					0.1
Accounts payable			(35.6)	[1]			(35.6)
Other current liabilities			(31.1)	[1],[2]			(31.2)	[2]
Other current liabilities					(0.1)	[2]
Deferred income taxes			(243.1)	[1]			(243.1)
Deferred income taxes
Other liabilities			(6.2)	[1]			(6.2)
Total liabilities assumed			(316.0)	[1]			(316.1)
Total liabilities assumed					(0.1)
Net assets acquired			1,353.6	[1]			1,353.6
Net assets acquired

[1] As previously reported in Ralcorp's 2010 Annual Report on Form 10-K.

[2] The adjustments to "Receivables", "Other current assets", "Other assets", and "Other current liabilities" reflect the identification and adjustment of unrecorded AIPC and Sepp's Gourmet Foods assets or liabilities at the acquisition date.

[3] The adjustments to "Inventories" and "Other intangible assets" reflects changes in the estimated fair value of AIPC's inventories and customer relationships based on the valuation analyses finalized late in the first quarter of fiscal 2011

[4] The adjustments to "Property" reflect changes in the estimated fair values for AIPC (increase of $1.5) and Sepp's Gourmet Foods (increase of $.1) based on the analyses finalized late in the first quarter of fiscal 2011.