Postretirement Benefit Plans - Pension Plans with Accumulated Benefit Obligation in Excess of Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2018	[1]	Dec. 31, 2017
Postemployment Benefits [Abstract]
Projected benefit obligation	$ 233.2		$ 107.8
Accumulated benefit obligation	231.0		105.4
Fair value of plan assets	$ 128.6		$ 0.0

[1] (a)In 2018, due to lower equity returns, one of our U.S. pension plans had accumulated benefit obligations in excess of plan assets as compared to prior year.