Unaudited Quarterly Results (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 2,061.8	[1]	$ 2,171.2	$ 2,072.2	$ 1,875.7	$ 2,110.0	$ 2,017.6	$ 1,743.0	$ 1,696.9	$ 8,180.9	$ 7,567.5	$ 9,820.6
Gross income	258.0	[1]	270.9	240.6	221.5	217.4	273.1	280.2	307.6	991.0	1,078.3	1,970.0
Operating income	89.2	[1]	122.9	78.5	75.4	77.1	128.5	132.9	169.5	366.0	508.0	1,424.8
Net income	78.9	[1]	75.7	38.0	39.3	38.0	68.6	67.7	99.0	231.9	273.4	790.0
Earnings (loss) attributable to Oshkosh Corporation common shareholders
Net income from continuing operations	77.6	[1]	74.7	39.2	39.0	40.3	70.2	68.3	100.2	230.5	279.0	816.0
Less: net earnings allocated to participating securities	(0.2)	[1]	(0.2)	(0.1)	(0.1)	0.1	0.1	0.1	0.1	(0.6)	(0.4)	(0.2)
Net income available to Oshkosh Corporation common shareholders	77.4	[1]	74.5	39.1	38.9	40.2	70.1	68.2	100.1	229.9	278.6	815.8
Net income (loss) from discontinued operations	$ 1.3	[1]	$ 1.0	$ (1.9)	$ (0.1)	$ (2.8)	$ (1.8)	$ (0.4)	$ (0.6)	$ 0.3	$ (5.6)	$ (26.0)
Earnings (loss) per share attributable to Oshkosh Corporation common shareholders-basic:
From continuing operations (in dollars per share)	$ 0.85	[1]	$ 0.82	$ 0.43	$ 0.43	$ 0.44	$ 0.77	$ 0.76	$ 1.11	$ 2.52	$ 3.07	$ 9.07
From discontinued operations (in dollars per share)	$ 0.01	[1]	$ 0.01	$ (0.02)	$ (0.01)	$ (0.03)	$ (0.02)	$ (0.01)	$ (0.01)	$ 0.00	$ (0.06)	$ (0.29)
Total earnings (loss) per share attributable to Oshkosh Corporation common shareholders-basic (in dollars per share)	$ 0.86	[1]	$ 0.83	$ 0.41	$ 0.42	$ 0.41	$ 0.75	$ 0.75	$ 1.10	$ 2.52	$ 3.01	$ 8.78
Earnings (loss) per share attributable to Oshkosh Corporation common shareholders-diluted:
From continuing operations (in dollars per share)	$ 0.85	[1]	$ 0.81	$ 0.43	$ 0.43	$ 0.44	$ 0.77	$ 0.75	$ 1.10	$ 2.51	$ 3.05	$ 8.97
From discontinued operations (in dollars per share)	$ 0.01	[1]	$ 0.01	$ (0.02)	$ (0.01)	$ (0.03)	$ (0.02)	$ (0.01)	$ (0.01)	$ 0.00	$ (0.06)	$ (0.28)
Total earnings (loss) per share attributable to Oshkosh Corporation common shareholders-diluted (in dollars per share)	$ 0.86	[1]	$ 0.82	$ 0.41	$ 0.42	$ 0.41	$ 0.75	$ 0.74	$ 1.09	$ 2.51	$ 2.99	$ 8.69
Common Stock per share dividends (in dollars per share)	$ 0	[1]	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

[1] The fourth quarter of 2012 was impacted by: (1) a $7.8 million change in estimate to increase revenue ($5.0 million, after-tax) resulting from the definitization of contracts in the defense segment (See Note 4 of the Notes to Consolidated Financial Statements), (2) a $7.0 million increase to selling, general and administrative expenses ($4.5 million, after-tax) resulting from the correction of a prior period error in the valuation of performance shares (See Note 17 of the Notes to Consolidated Financial Statements), (3) a $3.4 million increase to selling, general and administrative expenses ($2.2 million, after-tax) resulting from the curtailment of pension and other postretirement benefit plans (See Note 19 of the Notes to Consolidated Financial Statements), and (4) a decrease in income tax expense of $5.7 million related to the correction of deferred tax assets (See Note 20 of the Notes to Consolidated Financial Statements). Correction adjustments were not material to any individual prior period or the current period and, accordingly, the prior period results have not been adjusted.