Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive (income) loss		$ (27.9)	$ (28.9)	$ (23.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(9.1)	(12.0)
Amounts reclassified from accumulated other comprehensive income (loss)		(3.4)	(3.3)	(2.5)
Amounts reclassified from accumulated other comprehensive income (loss)		1.5	1.6
Net current period other comprehensive income (loss)		1.0	(5.7)
Amounts Reclassified from Accumulated OCI, Net of Tax and Noncontrolling Interest		10.1	6.3
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		(1.7)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		(12.0)	(8.0)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	[1]	(4.5)	(4.4)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	[1]	(11.3)	(6.3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		(15.8)	(10.7)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		(3.8)	(2.7)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		1.9	1.7
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	[1]	0.2	0.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	[1]	2.3	2.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		2.5	2.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		0.6	0.6
Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		(35.1)	(38.8)	(32.7)
Other comprehensive income before reclassifications		(8.3)	(14.1)
Amounts reclassified from accumulated other comprehensive income (loss)		3.4	3.3
Net current period other comprehensive income (loss)		3.7	(6.1)
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		(4.2)
Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		4.2	4.6	2.5
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(0.2)	2.1
Amounts reclassified from accumulated other comprehensive income (loss)		(0.2)	0.0
Net current period other comprehensive income (loss)		(0.4)	2.1
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		0.2
Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		3.6	5.3	7.0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0.0	0.0
Amounts reclassified from accumulated other comprehensive income (loss)		(1.7)	(1.7)
Net current period other comprehensive income (loss)		(1.7)	(1.7)
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		2.3
Settlement Cost [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		8.6	4.7
Settlement Cost [Member] | Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		8.6	4.7
Settlement Cost [Member] | Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		0.0	0.0
Settlement Cost [Member] | Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		0.0	0.0
Commodity Contract [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)			(0.6)	$ 0.0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Amounts reclassified from accumulated other comprehensive income (loss)		0.0	0.0
Amounts reclassified from accumulated other comprehensive income (loss)		(0.6)	0.0
Net current period other comprehensive income (loss)		(0.6)	0.0
Amounts removed from accumulated other comprehensive income due to deconsolidation		$ 0.0	$ 0.0

[1] These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 13 for additional information).