Retirement Benefit Plans (Analysis of plan assets) (Details) - Retirement Plans - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 585.0	$ 524.5	$ 430.2
Percentage of plan assets (percent)	100.00%	100.00%
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 22.4	$ 27.3
Percentage of plan assets (percent)	3.80%	5.20%
Fund investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 224.2	$ 207.3
Percentage of plan assets (percent)	38.30%	39.50%
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 193.6	$ 181.4
Percentage of plan assets (percent)	33.10%	34.60%
Government debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 15.0	$ 22.5
Percentage of plan assets (percent)	2.60%	4.30%
Guaranteed investments contracts
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 22.2	$ 13.2
Percentage of plan assets (percent)	3.80%	2.50%
Other assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 107.6	$ 72.8
Percentage of plan assets (percent)	18.40%	13.90%