Borrowing Arrangements (Narrative) (Details) (USD $)	12 Months Ended
Sep. 30, 2012	Sep. 30, 2011
Borrowing rate in addition to LIBOR	3.00%
Agreement termination date	August 2015
Debt instrument unused borrowing capacity fee, percentage	0.50%
Future maturities of outstanding borrowings
2013	$ 1,100,000
2014	1,000,000
2015	600,000
2016	200,000
2017	420,000,000
After 2017	202,500,000
ABL Agreement [Member]
Revolving credit facility amount	275,000,000
Potential increase size of the credit facility by an additional amount	150,000,000
Aggregate commitments availability	34,000,000
Aggregate commitments availability, percentage	12.50%
Outstanding letter of credit accrued fees and expenses	37,800,000
Excess availability reduced by outstanding borrowings, outstanding letters of credit and accrued fees and expenses	140,500,000
Swing Line Loans [Member]
Revolving credit facility amount	25,000,000
Letters Of Credit Outstanding [Member]
Revolving credit facility amount	60,000,000
8.75% Senior Unsecured Notes [Member]
Senior subordinated notes bear interest	8.75%	8.75%
Unamortized discount	2,600,000
Subordinated notes fair value	227,800,000
Redemption price applicable to prepayments of debt	103.00%
Principal amount not subject to optional prepayments	146,200,000
Percentage of purchase price	101.00%
7.375% Senior Subordinated Notes [Member]
Senior subordinated notes bear interest	7.375%	7.375%
Subordinated notes fair value	430,500,000
Redemption price applicable to prepayments of debt	101.00%
LIBOR [Member] \| Minimum [Member] \| ABL Agreement [Member]
Borrowing rate in addition to LIBOR	2.75%
LIBOR [Member] \| Maximum [Member]
Borrowing rate in addition to LIBOR	3.25%
Other Unspecified Base Rate [Member] \| Minimum [Member] \| ABL Agreement [Member]
Borrowing rate in addition to LIBOR	1.75%
Other Unspecified Base Rate [Member] \| Maximum [Member] \| ABL Agreement [Member]
Borrowing rate in addition to LIBOR	2.25%
Redemption At September 1, 2013 [Member] \| 8.75% Senior Unsecured Notes [Member]
Senior unsecured debt redemption price	22,500,000
Redemption Prior To September 2013 [Member] \| 8.75% Senior Unsecured Notes [Member]
Senior unsecured debt redemption price	$ 56,300,000
Redemption price applicable to prepayments of debt	108.75%

Amount of long-term debt prepayable by specified dates or upon the occurrence of specified events.

No definition available.

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Namespace Prefix:	mwa_
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Balance Type:	credit
Period Type:	instant

- Definition

Commitment fee rate as a percentage of the unused borrowing capacity under the long-term financing arrangement that is available to the entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
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Period Type:	duration

- Definition

Maximum excess availability level at which financial maintenance covenants would apply.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
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Period Type:	duration

- Definition

Maximum excess availability level at which financial maintenance covenants would apply, as a percentage of aggregate commitments.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
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- Definition

Total other amounts reducing excess availability.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Redemption price applicable to offer to redeem note in the event of a change in control of the Company.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Potential increase in the size of credit facility.

+ References

No definition available.

+ Details

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- Definition

Principal amount not subject to optional prepayments.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
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- Definition

Redemption price applicable to prepayments of debt.

+ References

No definition available.

+ Details

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Namespace Prefix:	mwa_
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Period Type:	duration

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

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-Topic 825

-SubTopic 10

-Section 50

-Paragraph 12

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number APB14-1

-Paragraph 31

-Subparagraph b

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 30

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-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

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- Definition

Reflects when the credit facility terminates, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount of long-term debt maturities after year five following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 10

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt maturing within the next twelve months following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates.

+ References

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- Definition

Amount of long-term debt maturing in year five following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

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- Definition

Amount of long-term debt maturing in year four following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

+ Details

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- Definition

Amount of long-term debt maturing in year three following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

+ Details

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- Definition

Amount of long-term debt maturing in year two following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates.

+ References

+ Details

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