Other Retirement Plans (Schedule of Covered Employees and Contributions, Multi-Employer Plans) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2014 USD ($) employee	Dec. 31, 2013 USD ($) employee	Dec. 31, 2012 USD ($) employee
Covered Employees and Contributions, Multi-Employer Plans [Line Items]
Multi-employer plans, contributions (in dollars)	$ 36.4	$ 48.2	$ 29.2
Multi-Employer Plans, Pension [Member]
Covered Employees and Contributions, Multi-Employer Plans [Line Items]
Multi-employer plans, contributions (in dollars)	31.9	44.6	27.9
Multi-Employer Plans, Postretirement Benefit [Member]
Covered Employees and Contributions, Multi-Employer Plans [Line Items]
Multi-employer plans, contributions (in dollars)	$ 4.5	$ 3.6	$ 1.3
Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees [Member] | Low [Member]
Covered Employees and Contributions, Multi-Employer Plans [Line Items]
Multi-employer plans, covered employees (in number of employees) | employee	590	778	308
Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees [Member] | High [Member]
Covered Employees and Contributions, Multi-Employer Plans [Line Items]
Multi-employer plans, covered employees (in number of employees) | employee	2,167	2,734	2,509