Accumulated Other Comprehensive Loss - Summary (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (312.1)
Other comprehensive income (loss) before reclassifications	(4.0)
Amounts reclassified from accumulated other comprehensive loss	347.4
Current period other comprehensive income	343.4
Ending balance	(263.8)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,939.5)
Ending balance	(3,596.1)
Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(826.6)
Other comprehensive income (loss) before reclassifications	0.1
Amounts reclassified from accumulated other comprehensive loss	(1.6)
Current period other comprehensive income	(1.5)
Ending balance	(828.1)
Postretirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,112.9)
Other comprehensive income (loss) before reclassifications	(4.1)
Amounts reclassified from accumulated other comprehensive loss	349.0
Current period other comprehensive income	344.9
Ending balance	$ (2,768.0)