Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (29.0)	$ (36.1)	$ (35.1)	$ (41.4)
Amounts reclassified from accumulated other comprehensive income (loss)	1.1	1.5
Net current period other comprehensive income (loss)	6.1	5.3
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(31.9)	(31.1)	(39.2)	(36.8)
Amounts reclassified from accumulated other comprehensive income (loss)	2.3	1.9
Net current period other comprehensive income (loss)	7.3	5.7
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Other Postretirement Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	2.5	(7.1)	2.5	(8.0)
Amounts reclassified from accumulated other comprehensive income (loss)	0.0	0.9
Net current period other comprehensive income (loss)	0.0	0.9
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0.1	0.1	0.1	0.1
Amounts reclassified from accumulated other comprehensive income (loss)	0.0	0.0
Net current period other comprehensive income (loss)	0.0	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Other Postretirement Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0.3	2.0	$ 1.5	$ 3.3
Amounts reclassified from accumulated other comprehensive income (loss)	(1.2)	(1.3)
Net current period other comprehensive income (loss)	(1.2)	(1.3)
Settlement Cost [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	5.0	3.8
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plan [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	5.0	3.8
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Other Postretirement Benefit Plan [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	0.0	0.0
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Other Postretirement Benefit Plan [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 0.0	$ 0.0