Commitments and Contingencies	12 Months Ended
Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies We are involved in various legal proceedings that have arisen in the normal course of operations, including the proceedings summarized below. The effect of the outcome of these matters on our financial statements cannot be predicted with certainty as any such effect depends on the amount and timing of the resolution of such matters. Other than the litigation described below, we do not believe that any of our outstanding litigation would have a material adverse effect on our business or prospects. Environmental. We are subject to a wide variety of laws and regulations concerning the protection of the environment, both with respect to the operations at many of our properties and with respect to remediating environmental conditions that may exist at our own or other properties. We accrue for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and reasonably estimable. In the acquisition agreement pursuant to which a predecessor to Tyco sold our businesses to a previous owner in August 1999, Tyco agreed to indemnify us and our affiliates, among other things, for all “Excluded Liabilities.” Excluded Liabilities include, among other things, substantially all liabilities relating to the time prior to August 1999, including environmental liabilities. The indemnity survives indefinitely. Tyco’s indemnity does not cover liabilities to the extent caused by us or the operation of our businesses after August 1999, nor does it cover liabilities arising with respect to businesses or sites acquired after August 1999. Since 2007, Tyco has engaged in multiple corporate restructurings, split-offs and divestitures. While none of these transactions directly affects the indemnification obligations of the Tyco indemnitors under the 1999 acquisition agreement, the result of such transactions is that the assets of, and control over, such Tyco indemnitors has changed. Should any of these Tyco indemnitors become financially unable or fail to comply with the terms of the indemnity, we may be responsible for such obligations or liabilities. On July 13, 2010, Rohcan Investments Limited, the former owner of property leased by Mueller Canada Ltd. and located in Milton, Ontario, filed suit against Mueller Canada Ltd. and its directors seeking C$10.0 million in damages arising from the defendants’ alleged environmental contamination of the property and breach of lease. Mueller Canada Ltd. leased the property from 1988 through 2008. We are pursuing indemnification from a former owner for certain potential liabilities that are alleged in this lawsuit, and we have accrued for other liabilities not covered by indemnification. On December 7, 2011, the Court denied the plaintiff’s motion for summary judgment. The purchaser of U.S. Pipe has been identified as a “potentially responsible party” (“PRP”) under the Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”) in connection with a former manufacturing facility operated by U.S. Pipe that was in the vicinity of a proposed Superfund site located in North Birmingham, Alabama. Under the terms of the acquisition agreement relating to our sale of U.S. Pipe, we agreed to indemnify the purchaser for certain environmental liabilities, including those arising out of the former manufacturing site in North Birmingham. Accordingly, the purchaser tendered the matter to us for indemnification, which we accepted. Ultimate liability for the site will depend on many factors that have not yet been determined, including the determination of EPA’s remediation costs, the number and financial viability of the other PRPs (there are four other PRPs currently) and the determination of the final allocation of the costs among the PRPs. Accordingly, because the amount of such costs cannot be reasonably estimated at this time, no amounts had been accrued for this matter at September 30, 2018. Walter Energy. We were a member of the Walter Energy federal tax consolidated group, through December 14, 2006, at which time the company was spun-off from Walter Industries. Until our spin-off from Walter Energy, we joined in the filing of the Walter Energy consolidated federal income tax return for each taxable year during which we were a member of the consolidated group. As a result, we are jointly and severally liable for the federal income tax liability, if any, of the consolidated group for each of those years. Accordingly, we could be liable in the event any such federal income tax liability is incurred, and not discharged, by any other member of the Walter Energy tax consolidated group for any period during which we were included in the Walter Energy tax consolidated group. In July 2015, Walter Energy filed for bankruptcy protection under Chapter 11 of the U.S. Bankruptcy Code in the Northern District of Alabama (“Chapter 11 Case”). On February 2, 2017, the Chapter 11 Case was converted to a liquidation proceeding under Chapter 7 of the U.S. Bankruptcy Code, pursuant to which Walter Energy is now in the process of being wound down and liquidated. The IRS is currently alleging that Walter Energy owes substantial amounts for prior taxable periods in which we were a member of the Walter Energy tax consolidated group (specifically, 1983-1994, 2000-2002 and 2005). On January 11, 2016, the IRS filed a proof of claim in the Chapter 11 Case, alleging that Walter Energy owes taxes,interest and penalties for the years 1983-1994, 2000-2002 and 2005 in an aggregate amount of $554.3 million ($229.1 million of which the IRS claims is entitled to priority status in the Chapter 11 Case). The IRS asserts that its claim is based on an alleged settlement of Walter Energy’s tax liability for years1983 through1994, which Walter Energy disputed. In the proof of claim, the IRS included an alternative calculation in an aggregate amount of $860.4 million, which it asserts would be appropriate in the event the alleged settlement is determined to be non-binding ($535.3 million of which the IRS claims is entitled to priority status in the Chapter 11 Case). The IRS has indicated its intent to pursue collection of amounts included in the proofs of claim from former members of the Walter Energy tax consolidated group. According to a quarterly report on Form 10-Q filed by Walter Energy with the SEC on November 5, 2015, Walter Energy had $33.0 million of accruals at September 30, 2015 for unrecognized tax benefits in connection with the matters subject to the IRS claims and Walter Energy stated it believed it had sufficient accruals to address any claims, including interest and penalties, and did not believe that any potential difference between any final settlements and amounts accrued would have a material effect on Walter Energy’s financial position, but such potential difference could be material to its results of operations in a future reporting period. We have been working constructively with the parties involved in this matter in an effort to reach a consensual resolution with respect to the alleged tax liabilities at issue. Based on our work to date, we believe that once certain anticipated refunds (applicable primarily to 1997 and 2006 through 2015) are applied against asserted income tax liabilities owing for other years, the total net tax liabilities of Walter Energy, if any, will be substantially less than those asserted by the IRS. We cannot estimate the amount of, or the extent to which we will be responsible for, any liabilities to which we may be subject relating to these tax claims. Such liabilities could have a material adverse effect on our business, financial condition, liquidity or results of operations. Furthermore, there can be no assurance we will be able to reach any resolution with the parties involved in this matter and, in such event, we would intend to vigorously assert any and all available defenses against any liabilities we may have as a member of the Walter Energy consolidated group. Indemnifications. We are a party to contracts in which it is common for us to agree to indemnify third parties for certain liabilities that arise out of or relate to the subject matter of the contract. In some cases, this indemnity extends to related liabilities arising from the negligence of the indemnified parties, but usually excludes any liabilities caused by gross negligence or willful misconduct. We cannot estimate the potential amount of future payments under these indemnities until events arise that would trigger a liability under the indemnities. Additionally, in connection with the sale of assets and the divestiture of businesses, such as the divestitures of U.S. Pipe and Anvil, we may agree to indemnify buyers and related parties for certain losses or liabilities incurred by these parties with respect to: (i) the representations and warranties made by us to these parties in connection with the sale and (ii) liabilities related to the pre-closing operations of the assets or business sold. Indemnities related to pre-closing operations generally include certain environmental and tax liabilities and other liabilities not assumed by these parties in the transaction. Indemnities related to the pre-closing operations of sold assets or businesses normally do not represent additional liabilities to us, but simply serve to protect these parties from potential liability associated with our obligations existing at the time of the sale. As with any liability, we have accrued for those pre-closing obligations that are considered probable and reasonably estimable. Should circumstances change, increasing the likelihood of payments related to a specific indemnity, we will accrue a liability when future payment is probable and the amount is reasonably estimable. Other Matters. We monitor and analyze our warranty experience and costs periodically and may revise our warranty reserves as necessary. Critical factors in our reserve analyses include warranty terms, specific claim situations, general incurred and projected failure rates, the nature of product failures, product and labor costs, and general business conditions. In 2017, our warranty analysis identified certain Technologies radio products produced prior to 2017 and installed in particularly harsh environments that had been failing at higher-than-expected rates. During the quarter ended March 31, 2017, we conducted additional testing of these products and revised our estimates of warranty expenses. As a result, we recorded an additional warranty expense of $9.8 million in the second quarter of 2017. During the quarter ended June 30, 2018, we completed a similar analysis and determined, based on this new information, that certain other Technologies products had been failing at higher-than-expected rates as well, and that the average cost to repair or replace certain products under warranty was higher than previously estimated. As a result, in the third quarter of 2018, we recorded an additional warranty expense of $14.1 million associated with such products. We are party to a number of other lawsuits arising in the ordinary course of business, including product liability cases for products manufactured by us or third parties. We provide for costs relating to these matters when a loss is probable and the amount is reasonably estimable. Administrative costs related to these matters are expensed as incurred. The effect of the outcome of these matters on our future financial statements cannot be predicted with certainty as any such effect depends on the amount and timing of the resolution of such matters. While the results of litigation cannot be predicted with certainty, we believe that the final outcome of such other litigation is not likely to have a materially adverse effect on our business or prospects. Operating Leases. We maintain operating leases primarily for equipment and facilities. Rent expense was $6.4 million, $5.8 million and $5.8 million for 2018, 2017 and 2016, respectively. Future minimum payments under non-cancellable operating leases are $4.3 million, $3.9 million, $3.5 million, $3.0 million and $2.0 million during 2019, 2020, 2021, 2022 and 2023, respectively. Total minimum payments due beyond 2023 are $3.2 million.

We are involved in various legal proceedings that have arisen in the normal course of operations, including the proceedings summarized below. The effect of the outcome of these matters on our financial statements cannot be predicted with certainty as any such effect depends on the amount and timing of the resolution of such matters. Other than the litigation described below, we do not believe that any of our outstanding litigation would have a material adverse effect on our business or prospects.

Environmental. We are subject to a wide variety of laws and regulations concerning the protection of the environment, both with respect to the operations at many of our properties and with respect to remediating environmental conditions that may exist at our own or other properties. We accrue for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and reasonably estimable.

In the acquisition agreement pursuant to which a predecessor to Tyco sold our businesses to a previous owner in August 1999, Tyco agreed to indemnify us and our affiliates, among other things, for all “Excluded Liabilities.” Excluded Liabilities include, among other things, substantially all liabilities relating to the time prior to August 1999, including environmental liabilities. The indemnity survives indefinitely. Tyco’s indemnity does not cover liabilities to the extent caused by us or the operation of our businesses after August 1999, nor does it cover liabilities arising with respect to businesses or sites acquired after August 1999. Since 2007, Tyco has engaged in multiple corporate restructurings, split-offs and divestitures.

While none of these transactions directly affects the indemnification obligations of the Tyco indemnitors under the 1999 acquisition agreement, the result of such transactions is that the assets of, and control over, such Tyco indemnitors has changed. Should any of these Tyco indemnitors become financially unable or fail to comply with the terms of the indemnity, we may be responsible for such obligations or liabilities.

On July 13, 2010, Rohcan Investments Limited, the former owner of property leased by Mueller Canada Ltd. and located in Milton, Ontario, filed suit against Mueller Canada Ltd. and its directors seeking C$10.0 million in damages arising from the defendants’ alleged environmental contamination of the property and breach of lease. Mueller Canada Ltd. leased the property from 1988 through 2008. We are pursuing indemnification from a former owner for certain potential liabilities that are alleged in this lawsuit, and we have accrued for other liabilities not covered by indemnification. On December 7, 2011, the Court denied the plaintiff’s motion for summary judgment.

The purchaser of U.S. Pipe has been identified as a “potentially responsible party” (“PRP”) under the Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”) in connection with a former manufacturing facility operated by U.S. Pipe that was in the vicinity of a proposed Superfund site located in North Birmingham, Alabama. Under the terms of the acquisition agreement relating to our sale of U.S. Pipe, we agreed to indemnify the purchaser for certain environmental liabilities, including those arising out of the former manufacturing site in North Birmingham. Accordingly, the purchaser tendered the matter to us for indemnification, which we accepted. Ultimate liability for the site will depend on many factors that have not yet been determined, including the determination of EPA’s remediation costs, the number and financial viability of the other PRPs (there are four other PRPs currently) and the determination of the final allocation of the costs among the PRPs. Accordingly, because the amount of such costs cannot be reasonably estimated at this time, no amounts had been accrued for this matter at September 30, 2018.

Walter Energy. We were a member of the Walter Energy federal tax consolidated group, through December 14, 2006, at which time the company was spun-off from Walter Industries. Until our spin-off from Walter Energy, we joined in the filing of the Walter Energy consolidated federal income tax return for each taxable year during which we were a member of the consolidated group. As a result, we are jointly and severally liable for the federal income tax liability, if any, of the consolidated group for each of those years. Accordingly, we could be liable in the event any such federal income tax liability is incurred, and not discharged, by any other member of the Walter Energy tax consolidated group for any period during which we were included in the Walter Energy tax consolidated group.

In July 2015, Walter Energy filed for bankruptcy protection under Chapter 11 of the U.S. Bankruptcy Code in the Northern District of Alabama (“Chapter 11 Case”). On February 2, 2017, the Chapter 11 Case was converted to a liquidation proceeding under Chapter 7 of the U.S. Bankruptcy Code, pursuant to which Walter Energy is now in the process of being wound down and liquidated.

The IRS is currently alleging that Walter Energy owes substantial amounts for prior taxable periods in which we were a member of the Walter Energy tax consolidated group (specifically, 1983-1994, 2000-2002 and 2005). On January 11, 2016, the IRS filed a proof of claim in the Chapter 11 Case, alleging that Walter Energy owes taxes,interest and penalties for the years 1983-1994, 2000-2002 and 2005 in an aggregate amount of $554.3 million ($229.1 million of which the IRS claims is entitled to priority status in the Chapter 11 Case). The IRS asserts that its claim is based on an alleged settlement of Walter Energy’s tax liability for years1983 through1994, which Walter Energy disputed. In the proof of claim, the IRS included an alternative calculation in an aggregate amount of $860.4 million, which it asserts would be appropriate in the event the alleged settlement is determined to be non-binding ($535.3 million of which the IRS claims is entitled to priority status in the Chapter 11 Case). The IRS has indicated its intent to pursue collection of amounts included in the proofs of claim from former members of the Walter Energy tax consolidated group.

According to a quarterly report on Form 10-Q filed by Walter Energy with the SEC on November 5, 2015, Walter Energy had $33.0 million of accruals at September 30, 2015 for unrecognized tax benefits in connection with the matters subject to the IRS claims and Walter Energy stated it believed it had sufficient accruals to address any claims, including interest and penalties, and did not believe that any potential difference between any final settlements and amounts accrued would have a material effect on Walter Energy’s financial position, but such potential difference could be material to its results of operations in a future reporting period.

We have been working constructively with the parties involved in this matter in an effort to reach a consensual resolution with respect to the alleged tax liabilities at issue. Based on our work to date, we believe that once certain anticipated refunds (applicable primarily to 1997 and 2006 through 2015) are applied against asserted income tax liabilities owing for other years, the total net tax liabilities of Walter Energy, if any, will be substantially less than those asserted by the IRS.

We cannot estimate the amount of, or the extent to which we will be responsible for, any liabilities to which we may be subject relating to these tax claims. Such liabilities could have a material adverse effect on our business, financial condition, liquidity or results of operations. Furthermore, there can be no assurance we will be able to reach any resolution with the parties involved in this matter and, in such event, we would intend to vigorously assert any and all available defenses against any liabilities we may have as a member of the Walter Energy consolidated group.

Indemnifications. We are a party to contracts in which it is common for us to agree to indemnify third parties for certain liabilities that arise out of or relate to the subject matter of the contract. In some cases, this indemnity extends to related liabilities arising from the negligence of the indemnified parties, but usually excludes any liabilities caused by gross negligence or willful misconduct. We cannot estimate the potential amount of future payments under these indemnities until events arise that would trigger a liability under the indemnities.

Additionally, in connection with the sale of assets and the divestiture of businesses, such as the divestitures of U.S. Pipe and Anvil, we may agree to indemnify buyers and related parties for certain losses or liabilities incurred by these parties with respect to: (i) the representations and warranties made by us to these parties in connection with the sale and (ii) liabilities related to the pre-closing operations of the assets or business sold. Indemnities related to pre-closing operations generally include certain environmental and tax liabilities and other liabilities not assumed by these parties in the transaction.

Indemnities related to the pre-closing operations of sold assets or businesses normally do not represent additional liabilities to us, but simply serve to protect these parties from potential liability associated with our obligations existing at the time of the sale. As with any liability, we have accrued for those pre-closing obligations that are considered probable and reasonably estimable. Should circumstances change, increasing the likelihood of payments related to a specific indemnity, we will accrue a liability when future payment is probable and the amount is reasonably estimable.

Other Matters. We monitor and analyze our warranty experience and costs periodically and may revise our warranty reserves as necessary. Critical factors in our reserve analyses include warranty terms, specific claim situations, general incurred and projected failure rates, the nature of product failures, product and labor costs, and general business conditions.

In 2017, our warranty analysis identified certain Technologies radio products produced prior to 2017 and installed in particularly harsh environments that had been failing at higher-than-expected rates. During the quarter ended March 31, 2017, we conducted additional testing of these products and revised our estimates of warranty expenses. As a result, we recorded an additional warranty expense of $9.8 million in the second quarter of 2017.

During the quarter ended June 30, 2018, we completed a similar analysis and determined, based on this new information, that certain other Technologies products had been failing at higher-than-expected rates as well, and that the average cost to repair or replace certain products under warranty was higher than previously estimated. As a result, in the third quarter of 2018, we recorded an additional warranty expense of $14.1 million associated with such products.

We are party to a number of other lawsuits arising in the ordinary course of business, including product liability cases for products manufactured by us or third parties. We provide for costs relating to these matters when a loss is probable and the amount is reasonably estimable. Administrative costs related to these matters are expensed as incurred. The effect of the outcome of these matters on our future financial statements cannot be predicted with certainty as any such effect depends on the amount and timing of the resolution of such matters. While the results of litigation cannot be predicted with certainty, we believe that the final outcome of such other litigation is not likely to have a materially adverse effect on our business or prospects.