Retirement Benefits (Summary of Changes in Pension Plan Assets Fair Value Classified as Level 3) (Details) - Defined Benefit Pension Plan - Level 3 - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 256.5	$ 254.1
Actual return on plan assets:
Assets held at end of year	(7.9)	2.4
Purchases, sales, and settlements, net	(2.0)
Fair Value at End of Year	$ 246.6	$ 256.5

No definition available.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

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