Employee Benefit and Retirement Plans - Summary of Reconciliation of Change in Fair Value Measurement of Defined Benefit Plans' Consolidated Assets Using Significant Unobservable Inputs (Level 3) (Detail) - Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 39.0	$ 26.9
Acquisitions		15.7
Realized gains (losses)	(0.7)	2.2
Unrealized (losses) gains	3.3	(2.5)
Purchases, sales, settlements and other, net	(8.6)	(3.3)
Fair value of plan assets at end of year	$ 33.0	$ 39.0