Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
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	$ 0.1	$ (1.9)
Long Term Indebtedness, Less than or Equal to			$ 750.0
Disposal Group, Including Discontinued Operation, Revenue	16.3	85.8
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net	3.3			$ 4.0
Disposal Group, Including Discontinued Operations, Taxes Applicable to Subsequent Years	1.7			2.3
Disposal Group, Including Discontinued Operation, Other Assets, Current	1.5			2.4
Disposal Group, Including Discontinued Operation, Intangible Assets	5.3			5.3
Disposal Group, Including Discontinued Operation, Assets	11.8			14.0
Disposal Group, Including Discontinued Operation, Accounts Payable	2.9			3.9
Disposal Group, Including Discontinued Operation, Accrued Income Tax Payable	2.4			3.1
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	3.7			5.2
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities	(33.8)			(39.8)
Disposal Group, Including Discontinued Operation, Taxes Payable	1.1			2.3
Disposal Group, Including Discontinued Operation, Pension Plan Benefit Obligation	9.6			9.7
Asset Retirement Obligation, Held for Sale	68.9			90.4
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent	6.7			6.6
Disposal Group, Including Discontinued Operation, Liabilities	61.5			$ 81.4
Disposal Group, Including Discontinued Operation, Costs of Goods Sold	(6.6)	(41.1)
Disposal Group, Including Discontinued Operation, Operating and Other Expenses	20.1	(24.7)
Disposal Group, Including Discontinued Operation, Asset Retirement Obligation, Revision of Estimate	22.5
Loss from discontinued operations before income taxes	29.8	20.0
Income tax expense / (benefit) from discontinued operations	4.3	3.5
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	25.6	14.6
Cash Provided by (Used in) Operating Activities, Discontinued Operations	8.1	9.0
Cash flows from investing activities for discontinued operations	$ 0.0	235.8
Subsidiaries [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long Term Indebtedness, Less than or Equal to			$ 750.0
AES Ohio Generation peakers [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		$ (1.9)