Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Change In Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	$ 717.9
Employer contributions	58.9	$ 162.3
Balance at end of year	868.0	717.9
Pension
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	717.9	638.1
Actual return on plan assets, net	131.3	(40.8)
Employer contributions	58.9	162.3
Gross benefits paid	(40.1)	(41.7)
Balance at end of year	868.0	717.9
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	2.0	1.0
Participants' contributions	1.2	0.3
Gross benefits paid	$ (3.2)	$ (1.3)