Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (312.1)	$ (1,228.3)
Amounts reclassified from accumulated other comprehensive income (loss)	197.3	22.1
Ending balance	(285.8)	(209.4)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,939.5)	(4,088.6)
Other comprehensive income (loss) before reclassifications	(13.0)
Amounts reclassified from accumulated other comprehensive income (loss)	197.3
Current period other comprehensive income (loss)	184.3
Ending balance	(3,755.2)	$ (4,082.7)
Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(826.6)
Other comprehensive income (loss) before reclassifications	(15.6)
Amounts reclassified from accumulated other comprehensive income (loss)	(2.3)
Current period other comprehensive income (loss)	(17.9)
Ending balance	(844.5)
Postretirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,112.9)
Other comprehensive income (loss) before reclassifications	2.6
Amounts reclassified from accumulated other comprehensive income (loss)	199.6
Current period other comprehensive income (loss)	202.2
Ending balance	$ (2,910.7)