Income Taxes Effective Tax Rate Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ 135.7	$ 68.4	$ 65.1
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	35.00%	35.00%	35.00%
State Income Taxes, net of federal effect	6.5	(5.0)	0.4
Effective Income Tax Rate Reconciliation, State Income Taxes, net of federal effect	1.60%	(2.60%)	0.20%
Income Tax Reconciliation, Share-based Compensation Cost	1.1	1.5	5.7
Effective Income Tax Rate Reconciliation, Share-based Compensation Cost	0.30%	0.70%	3.10%
Income Tax Reconciliation, Effect of rates different than statutory	(1.9)	(1.4)	(1.4)
Effective Income Tax Rate Reconciliation, Effect fo rates different than statutory	(0.50%)	(0.70%)	(0.80%)
Income Tax Reconciliation, Other Adjustments	1.4	(0.8)	(2.7)
Effective Income Tax Rate Reconciliation, Other Adjustments	0.40%	(0.30%)	(1.50%)
Income tax expense	$ 142.8	$ 62.7	$ 67.1
Effective Income Tax Rate	36.80%	32.10%	36.00%