Goodwill and Intangible Assets (Narrative) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Net	$ 471.0	$ 481.8	$ 276.8
Number of reporting units | Segment	8
Estimated cost of capital, minimum		10.00%
Estimated cost of capital, maximum		13.00%
Estimated cost of capital, weighted		10.90%
Hypothetical decrease to fair values of each reporting unit	10.00%
Net intangible assets	$ 471.0	$ 481.8
Intangibles with indefinite useful lives	69.8
Estimated amortization expense for intangible assets, current year	31.1
Finite-Lived Intangible Assets, Amortization Expense, Year Two	40.8
Finite-Lived Intangible Assets, Amortization Expense, Year Three	34.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four	34.3
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 260.5