Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (20.4)	$ (18.9)	$ (20.4)	$ (18.9)	$ (28.9)	$ (23.2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			1.2	1.2
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(0.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	0.6	0.0	0.6	0.0
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plan [Member]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	(28.3)	(27.1)	(28.3)	(27.1)	(38.8)	(32.7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			2.6	2.5
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	4.5	2.5	4.5	2.5	4.6	2.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(0.1)	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Pension Plan [Member]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	0.0	0.0	0.0	0.0	0.0	0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0.0	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Other Postretirement Benefits Plan [Member]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	4.0	$ 5.7	4.0	5.7	5.3	$ 7.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(1.3)	(1.3)
Defined Benefit Plans Income Loss [Member] | Pension Plan [Member]
Other Comprehensive Income (Loss), before Reclassifications, before Tax			0.0
Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Commodity Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ (0.6)		(0.6)		$ 0.0
Amounts removed from accumulated other comprehensive income due to deconsolidation			0.0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			0.0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax			(0.6)
Pension Plan [Member] | Defined Benefit Plan Prior Service Cost [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Settlement Cost [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			7.9	3.1
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			7.9	3.1
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0.0	0.0
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Pension Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0.0	0.0
Settlement Cost [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Other Postretirement Benefits Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			$ 0.0	$ 0.0