Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic benefit cost:
Recognition of net actuarial (gains) losses	$ 21.6	$ 11.9	$ 8.8	$ 21.1	$ 16.9	$ 18.5	$ (4.1)	$ 12.8
Accrued pension cost
Components of net periodic benefit cost:
Recognition of net actuarial (gains) losses						(16.9)	13.9	38.8
United States | Accrued pension cost
Components of net periodic benefit cost:
Service cost						10.7	10.7	12.6
Interest cost						21.0	23.5	24.0
Expected return on plan assets						(25.3)	(25.8)	(29.3)
Amortization of prior service cost						1.6	1.6	1.7
Recognition of net actuarial (gains) losses						(3.9)	(3.5)	30.0
Curtailment losses (gains)						0.9	0.0	(10.2)
Net periodic benefit (credit) cost						5.0	6.5	28.8
International Plans | Accrued pension cost
Components of net periodic benefit cost:
Service cost						1.8	1.5	1.7
Interest cost						5.5	7.3	7.2
Expected return on plan assets						(8.7)	(10.2)	(11.6)
Amortization of prior service cost						0.2	0.2	0.1
Recognition of net actuarial (gains) losses						20.1	17.4	8.8
Curtailment losses (gains)						0.0	0.0	0.0
Net periodic benefit (credit) cost						$ 18.9	$ 16.2	$ 6.2