Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax (benefit) expense	$ 13.0	$ 8.1
Total reclassifications for the period, net of tax	(34.4)	(21.2)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-operating expenses	5.0	6.5
Tax (benefit) expense	(1.3)	(1.7)
Total reclassifications for the period, net of tax	3.7	4.8
Actuarial Losses Recognized | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-operating expenses	5.0	6.9
Tax (benefit) expense	(1.3)	(1.8)
Total reclassifications for the period, net of tax	3.7	5.1
Prior Service Costs Recognized | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-operating expenses	0.0	(0.4)
Tax (benefit) expense	0.0	0.1
Total reclassifications for the period, net of tax	$ 0.0	$ (0.3)