Changes in Stockholders' Equity (Changes in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning of period	$ 2,993.5	$ 3,095.3
Net losses reclassified from accumulated other comprehensive loss	3.6	4.3
Other comprehensive income, net of reclassification adjustments	11.1	11.9
Balance end of period	3,019.0	3,119.4
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning of period	(282.4)
Other comprehensive (loss) income before reclassifications	0.0
Net losses reclassified from accumulated other comprehensive loss	3.0	3.1
Other comprehensive income, net of reclassification adjustments	3.0
Balance end of period	(279.4)
Deferred Net Gains (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning of period	1.4
Other comprehensive (loss) income before reclassifications	(4.7)
Net losses reclassified from accumulated other comprehensive loss	0.6
Other comprehensive income, net of reclassification adjustments	(4.1)
Balance end of period	(2.7)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning of period	(1,274.4)
Other comprehensive (loss) income before reclassifications	10.7
Net losses reclassified from accumulated other comprehensive loss	0.0
Other comprehensive income, net of reclassification adjustments	10.7
Balance end of period	(1,263.7)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning of period	(1,555.4)	(1,361.6)
Other comprehensive (loss) income before reclassifications	6.0
Net losses reclassified from accumulated other comprehensive loss	3.6
Other comprehensive income, net of reclassification adjustments	9.6
Balance end of period	$ (1,545.8)	$ (1,349.8)