Other Comprehensive (Loss) Income - Schedule of Reclassification From Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax		$ (63.7)	$ 52.7	$ 8.9
Investment and other income net		48.7	2.1	(43.9)
Net Realized Loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Selling, general and administrative expenses	[1]	2.8
Net Actuarial Loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of sales; Selling, general and administrative expenses	[2]	7.2	26.2	40.5
Translation Adjustments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before tax		2.8
Reclassifications, net of tax		2.8	0.0
Net Prior Service Credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of sales; Selling, general and administrative expenses	[2]	(2.8)	(12.7)	(26.9)
Curtailments and Settlements | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of sales; Selling, general and administrative expenses	[2]	1.6	78.9	0.2
Amortization of Pension and Other Postretirement Benefits Plan Cost
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before tax		6.0	92.4	13.8
Income tax expense (benefit)		1.7	39.7	4.9
Reclassifications, net of tax		4.3	$ 52.7	$ 8.9
Available-for-Sale Securities, Net Realized Gain on Equity Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before tax		(52.8)
Income tax expense (benefit)		18.0
Reclassifications, net of tax		(70.8)
Available-for-Sale Securities, Net Realized Gain on Equity Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Investment and other income net	[3]	$ 52.8

[1] Included within selling, general and administrative expenses in the Consolidated Statements of Operations.

[2] These accumulated other comprehensive (loss) income components are included in the calculation of net periodic pension and other postretirement benefits plan (income) expense recognized in cost of sales and selling, general and administrative expenses in the Consolidated Statements of Operations (see Note 9, Retirement Plans).

[3] Included within investment and other income-net in the Consolidated Statements of Operations