Deferral Of Employee Additional Cash Consideration If Compensation Exceeds Legislated Maximum Compensation, Percentage

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- Definition

Deferred Compensation Plan Gain (Loss) On Market Adjustment, Before Tax

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- Definition

Employee Service Share Based Compensation Awards Nonvested Total Compensation Cost Not Yet Recognized Period For Recognition.

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- Definition

Employer Matching Contribution Percentage, Deferred Compensation, Equity Option

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- Definition

Executive Savings Investment Plan, Matching, Vesting Percentage Per Year Of Service

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- Definition

Percentage Of Employee Cash Compensation Eligible For Deferral Under Executive Savings Investment Plan

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Total Share Based Liabilities Paid During Period

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- Definition

Share based compensation arrangement by share based payment award expiration

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Number of shares cash paid will be equal to.

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No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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-Name Statement of Financial Accounting Standard (FAS)

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

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- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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-Name Accounting Standards Codification

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 6, 7

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

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Equity-based compensation cost during the period with respect to the award, which will be recognized in income (as well as the total recognized tax benefit) or capitalized as part of the cost of an asset.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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-Publisher FASB

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- Definition

The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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Stock-Based Compensation Plans (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended																			12 Months Ended						12 Months Ended
	Sep. 30, 2011 years	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2011 Stock Options [Member] years	Sep. 30, 2010 Stock Options [Member]	Sep. 30, 2009 Stock Options [Member]	Sep. 30, 2011 Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2010 Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2009 Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2011 Restricted Stock Awards [Member]	Sep. 30, 2010 Restricted Stock Awards [Member]	Sep. 30, 2009 Restricted Stock Awards [Member]	Sep. 30, 2011 Other Stock-Based Compensation Awards [Member]	Sep. 30, 2010 Other Stock-Based Compensation Awards [Member]	Sep. 30, 2009 Other Stock-Based Compensation Awards [Member]	Sep. 30, 2011 Deferred Compensation [Member]	Sep. 30, 2010 Deferred Compensation [Member]	Sep. 30, 2009 Deferred Compensation [Member]	Sep. 30, 2011 Restricted Stock Units (RSUs) [Member]	Sep. 30, 2011 Minimum [Member] Stock Options [Member]	Sep. 30, 2011 Minimum [Member] Deferred Compensation [Member]	Sep. 30, 2011 Maximum [Member] Stock Options [Member]	Sep. 30, 2011 Maximum [Member] Deferred Compensation [Member]	Aug. 04, 2011 Post Foods Employees [Member]	Sep. 30, 2011 AIPC And Post Foods Employees [Member]	Sep. 30, 2011 Officer [Member]	Sep. 30, 2010 Officer [Member]	Sep. 30, 2009 Officer [Member]	Sep. 21, 2011 Officer [Member]	Sep. 30, 2011 Fiscal 2012 [Member] Restricted Stock Awards [Member]	Sep. 30, 2011 Fiscal 2013 [Member] Restricted Stock Awards [Member]	Sep. 30, 2011 Fiscal 2014 [Member] Restricted Stock Awards [Member]	Sep. 30, 2011 Fiscal 2015 [Member] Restricted Stock Awards [Member]	Sep. 30, 2011 Fiscal 2016 [Member] Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future awards	2,457,679
Stock-based liabilities paid	$ 1.0	$ 1.6	$ 0
Allocated share-based compensation expense	16.4	17.9	13.4
Stock-based compensation cost recognized													2.3	0.2	0.3											0	(1.0)	1.0
Deferred tax benefit	5.9	7.0	5.3
Compensation cost not yet recognized	19.4
Compensation cost not yet recognized, weighted average period of recognition, years	2.3
Award vesting period, years																				three		six
Maximum term for awards granted, years				10
Total intrinsic value of stock options exercised				12.9	9.9	17.0	3.0	0.3	0.2
Fair value of restricted stock awards vested										5.8	0.4	0.9
Number of shares cash paid will be equal to																								10,800	40,553				12,500
Awards outstanding										340,510	436,765								100,000											114,755	41,255	156,833	13,833	13,834
Employer maximum matching percentage on equity option																33.33%
Percentage of employee cash compensation eligible for deferral under executive savings investment plan																44.00%
Additional deferral of cash consideration percentage																					2.00%		6.00%
Executive savings investment plan, matching, vesting percentage per year of service	25.00%
Deferred compensation plan, compensation expenses																0.5	0.5	0.5
Pretax gain (loss) on market adjustment																$ (2.7)	$ 0.1	$ 1.3