Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (40.5)	$ (41.4)
Amounts reclassified from accumulated other comprehensive income (loss)	0.9
Net current period other comprehensive income (loss)	0.9
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plans, Defined Benefit [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(35.6)	(36.8)
Amounts reclassified from accumulated other comprehensive income (loss)	1.2
Net current period other comprehensive income (loss)	1.2
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Postretirement Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(7.4)	(8.0)
Amounts reclassified from accumulated other comprehensive income (loss)	0.6
Net current period other comprehensive income (loss)	0.6
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Pension Plans, Defined Benefit [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0.1	0.1
Amounts reclassified from accumulated other comprehensive income (loss)	0.0
Net current period other comprehensive income (loss)	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Postretirement Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	2.4	$ 3.3
Amounts reclassified from accumulated other comprehensive income (loss)	(0.9)
Net current period other comprehensive income (loss)	$ (0.9)