Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) numberOfEmployees	Sep. 30, 2019 USD ($) numberOfEmployees	Sep. 30, 2020 USD ($) numberOfEmployees	Sep. 30, 2019 USD ($) numberOfEmployees
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 8.9	$ 24.2	$ 25.0	$ 55.7
Pension Plan [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	7.2	23.0	19.5	51.7
Multiemployer Plans, Other Multiemployer [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 1.7	$ 1.2	$ 5.5	$ 4.0
Low [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | numberOfEmployees	1,452	3,814	1,119	1,626
High [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | numberOfEmployees	1,469	5,349	1,469	5,349