Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) employee	Jun. 30, 2019 USD ($) employee	Jun. 30, 2020 USD ($) employee	Jun. 30, 2019 USD ($) employee
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 9.0	$ 23.3	$ 16.1	$ 31.5
Pension Plan [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	6.9	21.8	12.3	28.8
Multiemployer Plans, Other Multiemployer [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer Plan, Employer Contribution, Cost	$ 2.1	$ 1.5	$ 3.8	$ 2.8
Low [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	1,424	2,117	1,119	1,626
High [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	1,469	5,349	1,469	5,349