Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($) employee	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($) employee
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, contributions (in dollars)	$ 31.0	$ 14.7	$ 37.3	$ 21.7
Multiemployer Plans, Pension [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, contributions (in dollars)	28.3	12.2	32.0	17.0
Multiemployer Plans, Other Multiemployer [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, contributions (in dollars)	$ 2.7	$ 2.5	$ 5.3	$ 4.7
Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees [Member] | Low [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	3,669	1,410	550	1,112
Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees [Member] | High [Member]
Covered Employees and Contributions, Multiemployer Plans [Line Items]
Multiemployer plans, covered employees (in number of employees) | employee	7,057	4,170	7,057	4,170