Summary of Activity Under Stock Plans (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Intrinsic value of options exercised	$ 26.9	$ 31.9	$ 13.4
Cash received from stock option exercises	53.8	60.9	19.7
Tax benefit related to stock award exercises	3.8	3.8	2.4
Stock-based compensation	13.0	15.1	13.2
Tax benefit related to stock-based compensation	$ 1.6	$ 1.9	$ 1.9

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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