Other Post-Employment Benefits and Other Employee Benefit Plans - One Percentage Point Change on Assumed Healthcare Cost (Detail) - Other Post-Employment Benefits and Other Employee Benefit Plans $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Effect on total of service and interest cost components, 1% Increase	$ 0.0
Effect on post-retirement benefit obligation, 1% Increase	0.3
Effect on total of service and interest cost components, 1% Decrease	0.0
Effect on post-retirement benefit obligation, 1% Decrease	$ (0.3)