Pension and Postretirement Benefit Plans-Company's Share of Expected Future Benefits Payments Schedule (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Pension
Schedule of Expected Future Pension Benefit Payment [Line Items]
2018	$ 11.2
2019	11.5
2020	12.0
2021	12.5
2022	12.9
2023 - 2027	76.2
Postretirement
Schedule of Expected Future Pension Benefit Payment [Line Items]
2018	1.5
2019	1.5
2020	1.4
2021	1.4
2022	1.3
2023 - 2027	$ 5.9

Schedule of Expected Future Pension Benefit Payment [Line Items]

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- Definition

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

+ 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 (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References

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- Definition

Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

+ References

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

+ References

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

+ References

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