Retirement Benefit Plans (Narrative) (Details) - Retirement Plans - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, cost recognized	$ 86,400,000	$ 73,500,000	$ 69,300,000
Accrued contributions	30,700,000	31,300,000
Expense recorded in relation to partial settlement of U.K. Pension Plan	8,000,000.0	(200,000)	3,100,000
Fair value of plan assets	585,000,000.0	$ 524,500,000	$ 430,200,000
Estimated amounts of contributions expected to be paid to the plans in next fiscal year	15,200,000
Annual benefits of plan participants that are covered by insurance contracts	$ 0