Retirement Benefit Plans - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amounts recognized on the Consolidated Balance Sheets:
Non-current assets	$ 2.0	$ 3.4
Accrued pension cost
Amounts recognized on the Consolidated Balance Sheets:
Current liabilities	(15.7)	(6.9)
U.S. Plans | Accrued pension cost
Amounts recognized on the Consolidated Balance Sheets:
Non-current assets	1.8	0.0
Current liabilities	(14.2)	(5.4)
Non-current liabilities	(97.4)	(109.1)
Total	(109.8)	(114.5)
International Plans | Accrued pension cost
Amounts recognized on the Consolidated Balance Sheets:
Non-current assets	0.2	3.4
Current liabilities	(1.5)	(1.5)
Non-current liabilities	(65.6)	(56.0)
Total	$ (66.9)	$ (54.1)