Fair Value Measurement - Assets Measured at Fair Value on a Nonrecurring Basis (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Goodwill, impairment charge	$ 21.3	$ 527.8
Impairment of intangible assets			$ 11.9
Total, impairment charge	22.4	558.3	36.5
Goodwill	588.5	602.0	1,085.7
Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-lived assets held and used, impairment charge			0.3
Long-lived assets held for sale or disposal, impairment charge	1.3	0.6	1.5
Goodwill, impairment charge	21.3	527.8	18.0
Impairment of intangible assets	0.2	29.7	11.9
Total, impairment charge	22.8	558.1	31.7
Goodwill		15.2
Other intangible assets, net book value		4.3
Total Assets		19.5
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-lived assets held for sale or disposal, fair value measurement	0.7		2.8
Goodwill, fair value measurement		15.2
Other intangible assets, fair value measurement		4.6
Total, fair value measurement	$ 0.7	$ 19.8	$ 2.8