Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	$ 0.0	$ 0.0	$ 4.5	$ 0.1
Disposal Group, Including Discontinued Operation, Revenue	0.9	16.2	23.3	56.7
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net					$ 18.0
Disposal Group, Including Discontinued Operation, Other Assets, Current					0.3
Disposal Group, Including Discontinued Operation, Assets					23.4
Disposal Group, Including Discontinued Operation, Accounts Payable					5.6
Disposal Group, Including Discontinued Operation, Other Liabilities, Current					3.1
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent					6.3
Disposal Group, Including Discontinued Operation, Liabilities					17.4
Disposal Group, Including Discontinued Operation, Operating and Other Expenses	0.5	(17.2)	(23.9)	(26.6)
Disposal Group, Including Discontinued Operation, Asset Retirement Obligation, Revision of Estimate				22.5
Cash Provided by (Used in) Operating Activities, Discontinued Operations	1.5	(1.7)	5.1	9.9
Disposal Group, Including Discontinued Operation, Inventory					3.7
Disposal Group, Including Discontinued Operation, Intangible Assets					0.1
Disposal Group, Including Discontinued Operation, Deferred Tax Assets					6.5
Disposal Group, Including Discontinued Operation, Accrued Income Tax Payable					0.3
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent					1.0
Disposal Group, Including Discontinued Operations, Asset Retirement Obligation					8.3
Disposal Group, Including Discontinued Operation, Accrued Property Taxes					0.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(19.7)	27.1	(13.6)	25.7
Property, Plant and Equipment, Additions	44.7	59.0	128.7	122.4
Payments for Removal Costs			1.0	0.0
Disposal GroupDisposal Group, Including Discontinued Operations, Taxes Applicable to Subsequent Years					$ 0.3
Loss from discontinued operations before income taxes	1.4	(1.0)	(0.6)	30.1
Income tax expense / (benefit) from discontinued operations	0.3	(0.2)	0.8	6.3
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	1.1	(0.8)	3.1	23.9
Cash Provided by (Used in) Operating Activities, Discontinued Operations	1.5	(1.7)	5.1	9.9
Cash flows from investing activities for discontinued operations	(0.4)		4.0
Subsidiaries [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 21.3	$ 37.7	49.7	$ 108.8
Conesville [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax			4.5
Payments for Removal Costs			1.0
Conesville [Member] | Forecast [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for Removal Costs			$ 4.0