Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ 635.4
Balance at end of period	648.1
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.7	$ 1.7
Other comprehensive income (loss)		(0.1)
Balance at end of period	1.7	1.6
Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(75.6)	(54.1)
Other comprehensive income (loss)	(0.2)	7.2
Balance at end of period	(75.8)	(46.9)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(134.0)	(129.0)
Other comprehensive income (loss)	1.7	1.9
Balance at end of period	(132.3)	(127.1)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.7	2.4
Other comprehensive income (loss)	(0.2)	(0.2)
Balance at end of period	1.5	2.2
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(206.2)	(179.0)
Other comprehensive income (loss)	1.3	8.8
Balance at end of period	$ (204.9)	$ (170.2)