Retirement Benefits Plans - Postretirement Benefit Plans Expense (Benefit) (Details) - Postretirement Benefit Plans - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Postretirement benefit plans benefit
Interest cost on benefit obligations	$ 0.3	$ 0.3	$ 0.6	$ 0.6
Amortization of:
Actuarial losses	0.2	0.2	0.4	0.4
Prior service benefit	(0.2)	(0.2)	(0.4)	(0.4)
Postretirement benefit plans benefit	$ 0.3	$ 0.3	$ 0.6	$ 0.6

Amortization of actuarial losses and prior service benefit.

No definition available.

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- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

+ References

+ Details

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- Definition

Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

+ Details

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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- Definition

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

+ References

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- References

No definition available.

+ Details

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- Details

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