Stockholders' Equity - Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ 682.5
Balance at end of period	699.6
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.8	$ 1.7
Balance at end of period	1.8	1.7
Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(67.4)	(76.8)
Other comprehensive income (loss)	1.3	(27.6)
Balance at end of period	(66.1)	(104.4)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(154.1)	(146.6)
Other comprehensive income (loss)	2.5	2.3
Balance at end of period	(151.6)	(144.3)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	0.3	1.0
Other comprehensive income (loss)	(0.2)	(0.2)
Balance at end of period	0.1	0.8
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(219.4)	(220.7)
Other comprehensive income (loss)	3.6	(25.5)
Balance at end of period	$ (215.8)	$ (246.2)