Receivables - Schedule of Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Receivables [Abstract]
Trade receivables - U.S. government	$ 105.8	$ 61.8
Trade receivables - other	734.0	997.7
Finance receivables	18.8	13.1
Notes receivable		0.4
Other receivables	17.1	32.0
Receivables, gross	875.7	1,105.0
Less allowance for doubtful accounts	(9.6)	(11.3)	$ (9.9)
Receivables, net	$ 866.1	$ 1,093.7

Represents the other trade receivables not elsewhere specified in the taxonomy.

No definition available.

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Namespace Prefix:	osk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the gross receivables of the entity, which may include trade receivables, finance receivables, notes receivables and other receivables before the allowance for doubtful accounts.

+ References

No definition available.

+ Details

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Namespace Prefix:	osk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the gross receivables of the entity, which may include trade receivables, finance receivables, notes receivables and other receivables net of allowance for doubtful accounts.

+ References

No definition available.

+ Details

Name:	osk_ReceivablesNet
Namespace Prefix:	osk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit loss on accounts receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
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+ Details

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of receivables that are derived from government contracts.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 310
-Section 45
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-URI http://asc.fasb.org/extlink&oid=118261985&loc=d3e55295-109406

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

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-Publisher FASB
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount due from parties in nontrade transactions, classified as other.

+ References

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-Publisher FASB
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+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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