Discontinued Operations (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended				12 Months Ended	1 Months Ended		3 Months Ended	12 Months Ended			12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2011 Post Shareholder [Member]	Sep. 30, 2011 Ralcorp Shareholder [Member]	Sep. 30, 2011 Trademarks [Member]	Jun. 30, 2011 Trademarks [Member]	Sep. 30, 2011 Trademarks [Member]	Sep. 30, 2011 Spin-Off [Member]	Sep. 30, 2011 Discontinued Operations [Member]	Sep. 30, 2010 Discontinued Operations [Member]	Sep. 30, 2011 Restated [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of pro rate share distribution from business unit Spin-Off	80.30%	80.30%			19.70%
Stock conversion ratio		2				1
Cash received from sale of discontinued operation										$ 900.0
Discontinued Operation, Period of Continuing Cash Flows after Disposal		two
Trademark impairment charges		557.5	19.4				106.6	32.1	106.6
Non-cash charge to reduce carrying value of goodwill	364.8		20.5										418.8
Deferred tax liabilities of discontinued operations, intangible assets	238.6	238.6	231.6								290.8	353.3
Deferred tax liabilities of discontinued operations, property	$ 131.6	$ 131.6	$ 115.8								$ 106.3	$ 116.1