Employee Retirement Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure
Amortization of prior service credits	$ 0.2
Pension Benefits
Defined Benefit Plan Disclosure
Contribution made to Pension Plan	16.2	$ 14.6
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	669.2	697.8	$ 707.7
Pre-tax cost to sponsor unfunded and non-qualified supplemental executive retirement plans	16.0	18.9	14.5
Net actuarial loss	14.0	21.3
Fair value of pension and other postretirement benefit contributions	0.0	0.0
Supplemental Employee Retirement Plans
Defined Benefit Plan Disclosure
Expected amortization of net actuarial losses	0.5
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	48.3	50.7
Settlement charge	2.1
Pre-tax cost to sponsor unfunded and non-qualified supplemental executive retirement plans	4.3	3.1	2.6
Net actuarial loss	4.3	11.3
Pension and other postretirement benefit contributions	0.1	1.3	0.4
Fair value of pension and other postretirement benefit contributions	34.3	31.8
U.S. Pension Plan \| Pension Benefits
Defined Benefit Plan Disclosure
Expected amortization of net actuarial losses	7.5
ABO for the pension plans	572.8	605.2
Contribution made to Pension Plan	$ 15.1	$ 11.4	$ 9.9

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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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.

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Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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Amount of payment for pension and other postretirement benefits.

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