Fair Value Measurements (Significant unobservable inputs, nonrecurring) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2017
Income Approach Valuation Technique [Member] | Minimum [Member] | Conesville [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(19.30%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	(54.30%)
Income Approach Valuation Technique [Member] | Minimum [Member] | Stuart [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(11.90%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	(61.40%)
Income Approach Valuation Technique [Member] | Minimum [Member] | Killen [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(14.20%)	(11.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	(56.60%)	(50.00%)
Income Approach Valuation Technique [Member] | Minimum [Member] | Peaking Generating Facilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)		(22.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent		(29.00%)
Income Approach Valuation Technique [Member] | Minimum [Member] | Hutchings Peakers [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(19.50%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	(40.30%)
Income Approach Valuation Technique [Member] | Maximum [Member] | Conesville [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	10.90%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	99.40%
Income Approach Valuation Technique [Member] | Maximum [Member] | Stuart [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	1.10%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	75.10%
Income Approach Valuation Technique [Member] | Maximum [Member] | Killen [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	2.90%	13.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	42.40%	67.00%
Income Approach Valuation Technique [Member] | Maximum [Member] | Peaking Generating Facilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)		17.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent		24.00%
Income Approach Valuation Technique [Member] | Maximum [Member] | Hutchings Peakers [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(25.90%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	63.10%
Income Approach Valuation Technique [Member] | Weighted Average [Member] | Conesville [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	0.60%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	20.20%
Income Approach Valuation Technique [Member] | Weighted Average [Member] | Stuart [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(4.70%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	8.00%		10.00%
Fair Value Inputs, Discount Rate	10.00%		7.00%
Income Approach Valuation Technique [Member] | Weighted Average [Member] | Killen [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(8.00%)	2.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	(15.50%)	6.00%	22.00%
Fair Value Inputs, Discount Rate	10.00%	11.00%	7.00%
Income Approach Valuation Technique [Member] | Weighted Average [Member] | Peaking Generating Facilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)		(3.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent		(4.00%)
Fair Value Inputs, Discount Rate		7.00%
Income Approach Valuation Technique [Member] | Weighted Average [Member] | Hutchings Peakers [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Annual revenue growth (percent)	(0.70%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent	12.10%
Fair Value Inputs, Discount Rate	7.00%
Fair Value, Inputs, Level 3 [Member] | AES Ohio Generation peakers [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-lived assets held and used, fair value			$ 237.5
Fair Value, Inputs, Level 3 [Member] | Killen [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-lived assets held and used, fair value	$ 84.3
Fair Value, Inputs, Level 3 [Member] | Peaking Generating Facilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Long-lived assets held and used, fair value	$ 5.2