Interest and Other Nonoperating Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Interest income					$ 5.6	$ 5.6	$ 6.9
Gain (loss) on equity securities	$ 8.1	$ 5.8			10.6	(2.9)	3.2
Foreign currency transaction losses					(3.6)	0.0	(15.5)
Derivative instrument losses			$ 7.7		(7.0)	0.0	0.0
Retirement benefit cost other than service cost					(37.9)	(52.7)	(39.7)
Interest on Colombia tax claim					0.0	(1.1)
Non-income taxes on intercompany billings					(4.6)	(4.2)	(2.6)
Venezuela operations					0.0	(0.9)	(0.6)
Gain on lease termination				$ 5.2	0.0	5.2
Gain on a disposition of a subsidiary					(4.1)	0.0	(11.2)
Other					(4.9)	(1.7)	(1.7)
Interest and other nonoperating income (expense)					(37.7)	$ (52.7)	(38.8)
French security services company
Investment [Line Items]
Gain on a disposition of a subsidiary	0.2		$ (4.7)		(4.5)
French airport security services company
Investment [Line Items]
Gain on a disposition of a subsidiary	$ (0.4)						$ (10.8)
COLOMBIA
Investment [Line Items]
Tax claim					$ 1.0