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Pension Benefit Obligations - Periodic Cost (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
United States |  |  |
Defined Benefit Plan |  |  |
Interest cost on projected benefit obligation | $ 9.8 | $ 4.7 | $ 4.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Expected return on plan assets | $ (5.8) | $ (5.6) | $ (6.5)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Amortization of net loss (gain) | $ 3.5 | $ 5.6 | $ 5.9
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Settlement (gain) loss recognized | $ (0.1) | $ 0.2 | $ 0.2
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Net periodic benefit cost (credit) | $ 7.4 | $ 4.9 | $ 3.9
International |  |  |
Defined Benefit Plan |  |  |
Service costs | 0.3 | 0.5 | 0.5
Interest cost on projected benefit obligation | $ 47.7 | $ 24.1 | $ 21.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Expected return on plan assets | $ (60.8) | $ (41.4) | $ (43.5)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Amortization of prior service costs (credits) | $ 0.1 | $ 0.1 | $ 0.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Amortization of net loss (gain) | $ (0.6) | $ 6.9 | $ 9.2
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Settlement (gain) loss recognized | $ 0.2 | $ 0.3 | $ 0.8
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Nonoperating Income | Other Nonoperating Income | Other Nonoperating Income
Net periodic benefit cost (credit) | $ (13.1) | $ (9.5) | $ (11.3)
Pension Plan, Defined Benefit |  |  |
Defined Benefit Plan |  |  |
Applicable deferred income taxes, included in OCI arising from net prior service cost and net gain/loss | $ 3.1 | $ 18.8 | $ 9.3

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