Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) employee	Jun. 30, 2020 USD ($) employee	Jun. 30, 2021 USD ($) employee	Jun. 30, 2020 USD ($) employee
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plan, employer contribution, cost	$ 29.7	$ 9.0	$ 54.4	$ 16.1
Pension
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plan, employer contribution, cost	21.7	6.9	44.2	12.3
Other Multiemployer
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plan, employer contribution, cost	$ 8.0	$ 2.1	$ 10.2	$ 3.8
Low
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	2,532	1,424	2,412	1,119
High
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	6,979	1,469	6,979	1,469