Interest and Other Nonoperating Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Interest income		$ 6.9	$ 4.1	$ 2.6
Gain on equity securities		3.2	1.5	0.5
Foreign currency transaction losses(a)		(15.5)	(7.6)	0.0
Derivative instruments		0.0	1.1	(0.6)
Retirement benefit cost other than service cost		(39.7)	(47.8)	(40.3)
Prepayment penalties		0.0	(8.3)	0.0
Interest on Brazil tax claim(c)		0.0	(1.6)	0.0
Non-income taxes on intercompany billings(d)		(2.6)	(1.3)	(1.0)
Gain on a disposition of a subsidiary(e)		11.2	0.0	0.0
Other		(2.3)	(0.3)	(0.3)
Total		$ (38.8)	(60.2)	$ (39.1)
Brazil tax claim	$ 11.1
Brazil
Investment [Line Items]
Brazil tax claim			$ 1.0