Retirement Benefit Plans (Breakdown of amount recognized in accumulated other comprehensive income) (Details) - Retirement Plans - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service cost/(credit)	$ 7.4	$ 6.1
Net actuarial loss/(gain)	144.4	145.4
Total	$ 151.8	$ 151.5

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

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- Definition

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.

+ References

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-Publisher FASB
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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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