Valuation Allowance Against Deferred Tax Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Allowances at beginning of year	$ 210.0	$ 177.7	$ 150.1
Benefits reserved current year	49.1	43.5	53.7
Benefits recognized current year	(117.0)	(13.8)	(5.2)
Write-offs and other changes	0.0	(0.5)	(0.2)
Translation difference	5.5	3.1	(20.7)
Allowances at end of year	$ 147.6	$ 210.0	$ 177.7