Stock-Based Compensation (Compensation Expense Included in General and Administrative Expenses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units [Member]
Compensation Expense Recognized Included in General and Administrative Expenses
Compensation expense	$ 13.4	$ 4.9	$ 7.1
Related income tax benefit	5.4	1.9	1.5
Stock Options [Member]
Compensation Expense Recognized Included in General and Administrative Expenses
Compensation expense	5.2	1.7	2.4
Related income tax benefit	$ 2.1	$ 0.7	$ 1.0