Retirement Benefits Plans (Components of the Changes in Benefit Obligations and Fair Value of Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Benefit Obligation
Current portion of retirement liabilities classified in accrued liabilities	$ 2.8	$ 2.9
Postretirement benefit plans
Change in Benefit Obligation
Benefit obligation at beginning of year	27.4	28.2
Interest cost	0.7	1.1	$ 1.0
Actuarial loss	2.0	1.0
Benefits paid	(2.6)	(2.9)
Benefit obligations at end of year	$ 27.5	$ 27.4	$ 28.2

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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- Definition

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

+ References

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- Definition

Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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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 cost recognized for passage of time related to defined benefit plan.

+ References

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- Definition

Amount of liability, recognized in statement of financial position, for pension, other postretirement and postemployment benefits, classified as current.

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