Summary of Post-Retirement Plans to Amortize from Accumulated Other Comprehensive Income (Loss) as Net Periodic Expense (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Pension Plans [Member]
Schedule Of Net Periodic Benefit Costs And Assumptions For Defined Benefit Retirement Plans [Line Items]
Net actuarial losses	$ 6.0
Net prior service costs	(0.3)
Total to be recognized as components of net periodic expense	5.7
Other Retirement Plans [Member]
Schedule Of Net Periodic Benefit Costs And Assumptions For Defined Benefit Retirement Plans [Line Items]
Net prior service costs	(0.3)
Total to be recognized as components of net periodic expense	$ (0.3)