Retirement Benefit Plans - Change in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets:
Company contributions / payments	$ 17.9	$ 35.4	$ 11.3
Accrued pension cost
Change in plan assets:
Fair value of plan assets at beginning of year	794.9
Company contributions / payments	17.9	35.4
Fair value of plan assets at end of year	866.1	794.9
U.S. Plans | Accrued pension cost
Change in plan assets:
Fair value of plan assets at beginning of year	520.2	448.3
Actual return on plan assets	85.8	104.2
Company contributions / payments	7.6	28.7
International plan exchange rate change	0.0	0.0
Benefits paid	(60.3)	(61.0)
Fair value of plan assets at end of year	553.3	520.2	448.3
Funded status at end of year	(109.8)	(114.5)
International Plans | Accrued pension cost
Change in plan assets:
Fair value of plan assets at beginning of year	274.7	254.6
Actual return on plan assets	32.5	21.9
Company contributions / payments	10.3	6.7
International plan exchange rate change	9.7	8.9
Benefits paid	(14.4)	(17.4)
Fair value of plan assets at end of year	312.8	274.7	$ 254.6
Funded status at end of year	$ (66.9)	$ (54.1)