Derivatives and Fair Value Measurements - Location and Amount of Gains and Losses on Derivatives Not Designated as Hedging Instruments Reported in Condensed Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivatives	$ (2.7)	$ 2.8
Derivatives Not Designated as Hedging Instruments under ASC 815 [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivatives	(1.8)	2.4
Derivatives Not Designated as Hedging Instruments under ASC 815 [Member] | Metal Commodity Contracts [Member] | Cost of Materials Sold [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivatives	(2.0)	1.6
Derivatives Not Designated as Hedging Instruments under ASC 815 [Member] | Crude oil commodity contracts [Member] | Warehousing, Delivery, Selling, General, and Administrative [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivatives		0.9
Derivatives Not Designated as Hedging Instruments under ASC 815 [Member] | Foreign Exchange Contracts [Member] | Other Income and (Expense), Net [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivatives	$ 0.2	$ (0.1)