Other Comprehensive (Loss) Income - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			$ (202.9)
Amounts reclassified from accumulated other comprehensive loss	$ 1.9	$ (96.9)	3.1	$ (67.6)
Other comprehensive loss	(39.9)	(64.4)	(18.4)	(87.0)
Ending Balance	(247.5)		(247.5)
Pension and Other Postretirement Benefits Plan Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(144.6)	(159.5)
Other comprehensive income (loss) before reclassifications			1.2
Amounts reclassified from accumulated other comprehensive loss			3.1	1.4
Other comprehensive loss	1.7	0.7	4.3	1.4
Ending Balance	(140.3)	(158.1)	(140.3)	(158.1)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			40.9	(15.5)
Other comprehensive income (loss) before reclassifications			(22.6)	28.8
Other comprehensive loss			(22.6)	28.8
Ending Balance	18.3	13.3	18.3	13.3
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(103.7)	(55.7)
Other comprehensive income (loss) before reclassifications			(21.4)	(19.7)
Amounts reclassified from accumulated other comprehensive loss			3.1	(67.6)
Other comprehensive loss			(18.3)	(87.3)
Ending Balance	$ (122.0)	(143.0)	$ (122.0)	(143.0)
Changes in the Fair Value of Available-for-Sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance				119.3
Other comprehensive income (loss) before reclassifications				(48.5)
Amounts reclassified from accumulated other comprehensive loss				(69.0)
Other comprehensive loss		(85.2)		(117.5)
Ending Balance		$ 1.8		$ 1.8