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
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (238.7)	$ (1,213.7)	$ (1,228.3)	$ (1,299.6)
Other comprehensive income (loss) before reclassifications			(8.2)
Amounts reclassified from accumulated other comprehensive income	42.2	35.2	106.5	104.9
Current period other comprehensive income			98.3
Ending balance	(200.3)	(1,117.4)	(200.3)	(1,117.4)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,036.6)	(4,010.9)	(4,088.6)	(4,084.8)
Ending balance	(3,990.3)	$ (3,998.0)	(3,990.3)	$ (3,998.0)
Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(872.9)
Other comprehensive income (loss) before reclassifications			(18.7)
Amounts reclassified from accumulated other comprehensive income			(17.8)
Current period other comprehensive income			(36.5)
Ending balance	(909.4)		(909.4)
Postretirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(3,215.7)
Other comprehensive income (loss) before reclassifications			10.5
Amounts reclassified from accumulated other comprehensive income			124.3
Current period other comprehensive income			134.8
Ending balance	$ (3,080.9)		$ (3,080.9)