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Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2025
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Prior service cost included in accumulated other comprehensive loss | $ 2.3 |  |  |
Prior service cost included in accumulated other comprehensive loss, net of tax | 1.7 |  |  |
Unrecognized net actuarial losses included in accumulated other comprehensive loss | 4.9 |  |  |
Unrecognized net actuarial losses included in accumulated other comprehensive loss, net of tax | $ 3.7 |  |  |
Health care cost trend rate |  |  |  |
Health care cost trend rate (as a percent) | 6.50% |  |  |
Increase in accumulated postretirement benefit obligation with 100 basis points increase in health care cost trend rate | $ 9.9 |  |  |
Increase in net periodic postretirement benefit cost with 100 basis points increase in health care cost trend rate | 0.8 |  |  |
Decrease in accumulated postretirement benefit obligation with 100 basis points decrease in health care cost trend rate | 7.5 |  |  |
Decrease in net periodic postretirement benefit cost with 100 basis points decrease in health care cost trend rate | 0.6 |  |  |
Defined benefit plan, expected future employer contributions, next fiscal year | $ 25.0 |  |  |
Multi-Employer Pension Plans |  |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | May 01, 2022 |  |  |
Maximum Percent of Total Plan Contributions Contributed to Multi-employer Plan | 5.00% | 5.00% | 5.00% |
Multiemployer plan period contributions | $ 1.5 | $ 1.4 | $ 1.3 |
401(k) plans |  |  |  |
Amounts expensed (income recognized) for matching and discretionary contributions | 39.5 | 43.3 | 42.9 |
Scenario Forecast |  |  |  |
Health care cost trend rate |  |  |  |
Health care cost trend rate (as a percent) |  |  |  | 5.00%
Supplemental Executive Retirement Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Trust held assets | 21.4 |  |  |
Defined contribution SERP expense | $ 1.6 | $ 1.6 | $ 2.0 |
Minimum |  |  |  |
401(k) plans |  |  |  |
Percentage contribution by employees for defined contribution 401(k) plans, low end of range (as a percent) | 2.00% |  |  |
Employer contribution | 2.00% |  |  |
Maximum |  |  |  |
401(k) plans |  |  |  |
Percentage contribution by employees for defined contribution 401(k) plans, low end of range (as a percent) | 100.00% |  |  |
Employer contribution | 6.00% |  |  |

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- Definition The amounts in accumulated other comprehensive income related to gains and losses that are not recognized immediately and are expected to be recognized as components of the net periodic benefit cost over the next fiscal year that follows the most recent annual statement of the financial position presented, net of tax. + References No definition available. + Details
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- Definition The amounts in accumulated other comprehensive income related to the prior service cost or credit expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of the financial position presented, net of tax. + References No definition available. + Details
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- Definition Defined benefit plan, expected future employer contributions, next fiscal year. + References No definition available. + Details
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- Definition Maximum percent of plan contributions contributed to multi-employer plan. + References No definition available. + Details
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- Definition The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(b)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 + Details
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- Definition Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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