Pension and Other Postretirement Benefits - Expected Future Benefit Payments and Related Federal Subsidy Receipts (Details) $ in Millions	Sep. 30, 2024 USD ($)
Pension Benefits
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Year 1	$ 31.6
Year 2	32.7
Year 3	34.0
Year 4	34.9
Year 5	36.3
Year 6 and thereafter	206.0
Pension Benefits \| SERP
Disclosure of Expected Gross Prescription Drug Subsidy Receipts [Abstract]
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	9.5
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	9.5
Other Benefits
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Year 1	3.4
Year 2	3.4
Year 3	3.4
Year 4	3.5
Year 5	3.4
Year 6 and thereafter	17.3
Disclosure of Expected Gross Prescription Drug Subsidy Receipts [Abstract]
Year 1	0.1
Year 2	0.1
Year 3	0.2
Year 4	0.2
Year 5	0.2
Years 6 and thereafter	$ 0.9

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Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fifth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.

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Amount of projected benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
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Amount of prescription drug subsidy receipt expected after fifth fiscal year following current fiscal year.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Amount of prescription drug subsidy receipt expected in next fiscal year following current fiscal year.

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Amount of prescription drug subsidy receipt expected in fourth fiscal year following current fiscal year.

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Amount of prescription drug subsidy receipt expected in third fiscal year following current fiscal year.

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Amount of prescription drug subsidy receipt expected in second fiscal year following current fiscal year.

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