Stock-Based Compensation (Schedule of Stock-based Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets:
Diversified investments associated with the ESU program, current	$ 3.6	$ 3.1
Diversified investments associated with the ESU program, long-term	46.8	39.7
Diversified investments associated with the ESU program, total	50.4	42.8
Liabilities:
Share liabilities, current	3.7	3.1
Share liabilities, long-term	11.2	10.8
Other - primarily timing differences between employee withholdings and related employer contributions to be submitted to various plans' trust accounts, current	5.5	5.9
Other - primarily timing differences between employee withholdings and related employer contributions to be submitted to various plans' trust accounts, long-term	0.0	0.0
Other - primarily timing differences between employee withholdings and related employer contributions to be submitted to various plans' trust accounts, total	5.5	5.9
Total liabilities associated with stock-based compensation, current	9.3	9.0
Total liabilities associated with stock-based compensation, long-term	50.5	42.2
Total liabilities associated with stock-based compensation, total	59.8	51.2
ESU program
Liabilities:
Share liabilities, current	3.7	3.1
Share liabilities, long-term	48.7	40.9
Share liabilities, total	52.4	44.0
PSU awards
Liabilities:
Share liabilities, current	0.1	0.0
Share liabilities, long-term	1.8	1.3
Share liabilities, total	$ 1.9	$ 1.3