Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (41.2)		$ (41.4)
Amounts reclassified from accumulated other comprehensive income (loss)	(0.4)	(0.4)
Amounts reclassified from accumulated other comprehensive income (loss)	0.2	0.3
Amounts reclassified from accumulated other comprehensive income (loss)	0.2
Net current period other comprehensive income (loss)	0.2
Pension Plans, Defined Benefit [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	0.4	0.4
Postretirement Benefit Plan [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	(0.2)	(0.2)
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	(36.4)		(36.8)
Amounts reclassified from accumulated other comprehensive income (loss)	0.4
Net current period other comprehensive income (loss)	0.4
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	(7.8)		(8.0)
Amounts reclassified from accumulated other comprehensive income (loss)	0.2
Net current period other comprehensive income (loss)	0.2
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
Net current period other comprehensive income (loss)	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	2.9		3.3
Amounts reclassified from accumulated other comprehensive income (loss)	(0.4)
Net current period other comprehensive income (loss)	$ (0.4)