Retirement Benefit Plans - Change in Benefit Obligation (Details) - Accrued pension cost - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Actuarial losses	$ (16.2)
U.S. Plans
Change in benefit obligation:
Benefit obligation at beginning of year	634.7	$ 586.6
Service cost	10.7	10.7	$ 12.6
Interest cost	21.0	23.5	24.0
Plan amendments	0.1	0.0
Actuarial losses	56.6	74.9
International plan exchange rate change	0.0	0.0
Curtailments	0.3	0.0
Benefits paid	(60.3)	(61.0)
Acquisitions	0.0	0.0
Benefit obligation at end of year	663.1	634.7	586.6
International Plans
Change in benefit obligation:
Benefit obligation at beginning of year	328.8	300.3
Service cost	1.8	1.5	1.7
Interest cost	5.5	7.3	7.2
Plan amendments	0.0	0.0
Actuarial losses	43.9	29.1
International plan exchange rate change	14.1	7.6
Curtailments	0.0	0.0
Benefits paid	(14.4)	(17.4)
Acquisitions	0.0	0.4
Benefit obligation at end of year	$ 379.7	$ 328.8	$ 300.3