Retirement Benefit Plans - Changes in Plan Assets and Benefit Obligations in AOCL (Details) - Accrued pension cost - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
U.S. Plans
Changes in prior service cost recognized in accumulated other comprehensive loss:
Accumulated other comprehensive income at beginning of year	$ 4.8	$ 6.4
Prior service cost	0.1	0.0
Recognized prior service credit	(1.6)	(1.6)
Loss recognized due to curtailment	(0.6)	0.0
Foreign currency impact	0.0	0.0
Total recognized in accumulated other comprehensive income at December 31	2.7	4.8
International Plans
Changes in prior service cost recognized in accumulated other comprehensive loss:
Accumulated other comprehensive income at beginning of year	3.9	4.0
Prior service cost	0.0	0.0
Recognized prior service credit	(0.2)	(0.2)
Loss recognized due to curtailment	0.0	0.0
Foreign currency impact	0.2	0.1
Total recognized in accumulated other comprehensive income at December 31	$ 3.9	$ 3.9