Retirement Benefit Plans - Narrative (Details) $ in Millions	3 Months Ended						12 Months Ended
	Dec. 31, 2020 USD ($) shares	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2021	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Company contributions / payments								$ 17.9	$ 35.4	$ 11.3
Recognition of net actuarial losses (gains)	$ (21.6)	$ (11.9)	$ (8.8)	$ (21.1)	$ (16.9)			(18.5)	4.1	(12.8)
Curtailment gain						$ 10.2
Return on plan assets								$ 27.1	27.9	23.7
Company common stock | shares	1,095,124							1,095,124
Fair value of company common stock	$ 84.7							$ 84.7
Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Company contributions / payments								17.9	35.4
Actuarial losses								16.2
Recognition of net actuarial losses (gains)								16.9	(13.9)	(38.8)
Accumulated benefit obligations	515.9							515.9
Current liabilities	15.7			6.9				15.7	6.9
Projected benefit obligation	521.2							521.2
Fair value of plan assets	343.4							343.4
Pension accumulated benefit obligation	1,026.3			942.0				1,026.3	$ 942.0
Percentage increase in value									16.50%
Defined benefit plan, plan assets, amount	$ 866.1			$ 794.9				866.1	$ 794.9
Employee Stock
Defined Benefit Plan Disclosure [Line Items]
Dividends								1.5	2.3	2.9
U.S. Plans | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Company contributions / payments								7.6	28.7
Deferred compensation								24.0
Actuarial losses								(56.6)	(74.9)
Recognition of net actuarial losses (gains)								$ 3.9	$ 3.5	$ (30.0)
Discount rate	2.84%			3.50%		4.36%		2.84%	3.50%	4.36%	3.80%
Discount rate								3.50%
Expected long-term return on plan assets								5.22%
Percentage of defined benefit plan obligation in US								64.00%
Defined benefit pension plan percentage of fair value of plan assets								64.00%
Current liabilities	$ 14.2			$ 5.4				$ 14.2	$ 5.4
Defined benefit plan, plan assets, amount	553.3			$ 520.2		$ 448.3		553.3	520.2	$ 448.3
U.S. Plans | Accrued pension cost | Forecast
Defined Benefit Plan Disclosure [Line Items]
Discount rate							2.84%
Expected long-term return on plan assets							4.69%
International Plans | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Company contributions / payments								10.3	6.7
Actuarial losses								(43.9)	(29.1)
Recognition of net actuarial losses (gains)								(20.1)	$ (17.4)	(8.8)
Discount rate				0.75%					0.75%
Current liabilities	1.5			$ 1.5				1.5	$ 1.5
Defined benefit plan, plan assets, amount	312.8			274.7		$ 254.6		312.8	274.7	254.6
International Plans | Accrued pension cost | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	265.0			231.8				265.0	231.8
Discount Rate In Dollars | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Recognition of net actuarial losses (gains)								88.0	100.9	83.4
Other Valuation Assumptions | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Recognition of net actuarial losses (gains)								4.4	3.1	62.4
Return on Plan Assets vs. Expectation | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Recognition of net actuarial losses (gains)								$ 84.3	$ 90.1	$ 17.8
Discount Rate In Basis Points | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Decrease to discount rate								66	86	56
Overfunded Plan | Accrued pension cost
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 2.0			$ 3.4				$ 2.0	$ 3.4