Basis of Presentation and Accounting Policies (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Reconciled Basic and Diluted EPS
Net income	$ 206.0us-gaap_NetIncomeLoss	$ 180.3us-gaap_NetIncomeLoss	$ 420.2us-gaap_NetIncomeLoss	$ 378.4us-gaap_NetIncomeLoss
Less: Allocation to participating securities	(0.2)	(0.2)	(0.4)	(0.5)
Net income available to common shareowners	$ 205.8	$ 180.1	$ 419.8	$ 377.9
Basic weighted average outstanding shares	134.9	138.5	135.3	138.5
Effect of dilutive securities
Stock options	1.1	1.5	1.1	1.5
Performance shares	0	0.2	0.1	0.2
Diluted weighted average outstanding shares	136.0	140.2	136.5	140.2
Earnings Per Share, Basic [Abstract]
Basic	$ 1.53us-gaap_EarningsPerShareBasic	$ 1.30us-gaap_EarningsPerShareBasic	$ 3.10us-gaap_EarningsPerShareBasic	$ 2.73us-gaap_EarningsPerShareBasic
Earnings Per Share, Diluted [Abstract]
Diluted	$ 1.51us-gaap_EarningsPerShareDiluted	$ 1.28us-gaap_EarningsPerShareDiluted	$ 3.08us-gaap_EarningsPerShareDiluted	$ 2.70us-gaap_EarningsPerShareDiluted

Net income available to common stockholders for purposes of calculating earnings per share under the two-class method.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of call options and warrants using the treasury stock method.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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