Other Comprehensive (Loss) Income - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			$ (92.2)
Amounts reclassified from accumulated other comprehensive loss	$ 1.7	$ (6.4)	(65.9)	$ 55.2
Other comprehensive income (loss)	16.6	(23.8)	(70.4)	(22.3)
Ending Balance	(163.0)		(163.0)
Changes in the Fair Value of Available-for-Sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			119.3
Other comprehensive (loss) income before reclassifications			(48.5)
Amounts reclassified from accumulated other comprehensive loss	(1.8)		(70.8)
Other comprehensive income (loss)			(119.3)
Ending Balance	0.0		0.0
Pension and Other Postretirement Benefits Plan Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(159.5)	(727.5)
Other comprehensive (loss) income before reclassifications			0.0	(69.7)
Amounts reclassified from accumulated other comprehensive loss	0.7	(6.4)	2.1	55.2
Amounts reclassified due to disposition of a business				1.2
Other comprehensive income (loss)			2.1	(13.3)
Ending Balance	(157.4)	(740.8)	(157.4)	(740.8)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(15.5)	(65.7)
Other comprehensive (loss) income before reclassifications			43.6	(8.5)
Amounts reclassified from accumulated other comprehensive loss	2.8		2.8	0.0
Amounts reclassified due to disposition of a business				(0.7)
Other comprehensive income (loss)			46.4	(9.2)
Ending Balance	30.9	(74.9)	30.9	(74.9)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(55.7)	(793.2)
Other comprehensive (loss) income before reclassifications			(4.9)	(78.2)
Amounts reclassified from accumulated other comprehensive loss			(65.9)	55.2
Amounts reclassified due to disposition of a business				0.5
Other comprehensive income (loss)			(70.8)	(22.5)
Ending Balance	$ (126.5)	$ (815.7)	$ (126.5)	$ (815.7)