Accumulated Other Comprehensive Loss - Amounts Reclassified Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other (expense), net	$ (24.2)	$ (32.5)	$ (434.6)	$ (134.3)
Total before tax	(7.6)	(7.2)	(352.1)	(115.9)
Income tax benefit	(10.9)	(6.1)	33.8	(26.6)
Total reclassifications for the period	(18.5)	(13.3)	(318.3)	(142.5)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	41.4	43.6	427.4	110.6
Income tax benefit	(1.4)	(1.4)	(40.0)	(4.1)
Total reclassifications for the period	40.0	42.2	387.4	106.5
Reclassification out of Accumulated Other Comprehensive Income | Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other (expense), net	(1.3)	0.6	(2.9)	(17.8)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior service cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other (expense), net	(1.6)	(1.5)	(4.7)	(4.4)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other (expense), net	44.3	44.5	134.3	132.8
Reclassification out of Accumulated Other Comprehensive Income | Settlement losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other (expense), net	$ 0.0	$ 0.0	$ 300.7	$ 0.0