Retirement Benefit Plans - Employer Contributions to Defined Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employer Contributions [Abstract]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 35.4	$ 11.3	$ 11.5
Pension Plan [Member]
Employer Contributions [Abstract]
Defined Benefit Plan, Plan Assets, Contributions by Employer	35.4	$ 11.3
2018 (planned)	$ 11.8