Accumulated Other Comprehensive Income - Amounts Reclassified Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense), net	$ (22.6)	$ (32.9)	[1]
Postretirement Plans:
Total reclassification for the period	38.7	34.9
Translation Adjustments
Postretirement Plans:
Total reclassification for the period	0.0
Amortization of prior service cost
Postretirement Plans:
Amortization of postretirement plan items, before tax	(1.8)	(1.4)
Amortization of actuarial losses
Postretirement Plans:
Amortization of postretirement plan items, before tax	41.8	43.3
Postretirement Plans
Postretirement Plans:
Amortization of postretirement plan items, before tax	40.0	36.6
Income tax benefit	(1.3)	(1.7)
Total reclassification for the period	38.7
Adjustment for substantial completion of liquidation of foreign subsidiaries | Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense), net	$ 0.0	$ (5.3)

[1] *Amounts were changed to conform to the current-year presentation. See Note 3.