Interest and Other Nonoperating Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Interest income		$ 4.1	$ 2.6	$ 3.3
Gain on available-for-sale securities		1.5	0.5	1.1
Foreign currency transaction losses		(7.6)	0.0	0.0
Derivative instruments		1.1	(0.6)	(0.5)
Retirement benefit cost other than service cost		(47.8)	(40.3)	(39.8)
Prepayment penalties		(8.3)	0.0	0.0
Interest on Brazil tax claim(b)		(1.6)	0.0	0.0
Other		(1.6)	(1.3)	(0.5)
Total		(60.2)	$ (39.1)	$ (36.4)
Brazil tax claim	$ 11.1
Brazil
Investment [Line Items]
Brazil tax claim		$ 1.0