Fair Value (Nonrecurring Unobservable Inputs) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value		$ 63,000,000
Laurel Mountain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		30,000,000
Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		5,000,000
Fair Value | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		$ 214,000,000
Long Lived Assets Held And Used [Member] | Buffalo Gap [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring			$ 36,000,000
Long Lived Assets Held And Used [Member] | buffalo gap II [Member] [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring			92,000,000
Long Lived Assets Held And Used [Member] | Fair Value | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring	[1]		$ 0
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(70.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(70.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		467.00%
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(1.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		48.00%
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(15.00%)
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		37.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		82.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		59.00%
Measurement Input, Discount Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		10.00%
Measurement Input, Discount Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		12.00%

[1] See Note 20—Asset Impairment Expense for further information.