Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period			$ 424.4
Balance at end of period	$ 650.0		650.0
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.6	$ 1.7	1.7	$ 1.7
Other comprehensive income (loss)			(0.1)
Balance at end of period	1.6	1.7	1.6	1.7
Interest Rate Swap
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period		(1.1)		(1.2)
Other comprehensive income (loss)		(0.7)		(1.2)
Less reclassification adjustment for amounts included in interest expense		1.8		2.4
Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(63.6)	(73.8)	(54.1)	(88.5)
Other comprehensive income (loss)	2.9	19.3	(6.6)	34.0
Balance at end of period	(60.7)	(54.5)	(60.7)	(54.5)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(125.2)	(134.4)	(129.0)	(137.0)
Other comprehensive income (loss)	1.9	1.8	5.7	4.4
Balance at end of period	(123.3)	(132.6)	(123.3)	(132.6)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	2.0	2.7	2.4	3.1
Other comprehensive income (loss)	(0.2)	(0.2)	(0.6)	(0.6)
Balance at end of period	1.8	2.5	1.8	2.5
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(185.2)	(204.9)	(179.0)	(221.9)
Other comprehensive income (loss)	4.6	22.0	(1.6)	39.0
Balance at end of period	$ (180.6)	$ (182.9)	$ (180.6)	$ (182.9)