Retirement Benefit Plans - Employer Contributions to Defined Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employer Contributions [Abstract]
Employer Contributions to Defined Benefit Plans	$ 17.9	$ 35.4	$ 11.3
Accrued pension cost
Employer Contributions [Abstract]
Employer Contributions to Defined Benefit Plans	17.9	$ 35.4
2021 (estimated)	$ 16.0