Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) numberOfEmployees	Mar. 31, 2020 USD ($) numberOfEmployees
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 24.7	$ 7.1
Pension Plan [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	22.5	5.4
Multiemployer Plans, Other Multiemployer [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 2.2	$ 1.7
Low [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | numberOfEmployees	2,412	1,119
High [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | numberOfEmployees	2,532	1,424