Accumulated Other Comprehensive Loss - Amounts Reclassified Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other expense, net	$ (32.5)	$ (49.2)	$ (134.3)	$ (108.5)
Total reclassifications for the period	42.2	35.2	106.5	104.9
Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period			(17.8)
Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of postretirement plan items, before tax	43.6	36.2	110.6	107.9
Income tax benefit	(1.4)	(1.0)	(4.1)	(3.0)
Total reclassifications for the period			124.3
Amortization of prior service cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of postretirement plan items, before tax	(1.5)	(1.4)	(4.4)	(4.4)
Amortization of actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of postretirement plan items, before tax	44.5	37.6	132.8	112.3
Adjustment for substantial completion of liquidation of foreign subsidiaries | Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other expense, net	$ 0.6	$ 0.0	$ (17.8)	$ 0.0