Asset Impairment Expense (Narrative) (Details)		3 Months Ended				6 Months Ended		8 Months Ended		9 Months Ended	12 Months Ended
		Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($) project	Aug. 31, 2016 USD ($)	Aug. 28, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) project	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Debt Instrument [Line Items]
Other Asset Impairment Charges											$ 1,096,000,000	$ 285,000,000	$ 91,000,000
Buffalo Gap I
Debt Instrument [Line Items]
Assets, fair value		$ 36,000,000									36,000,000
Other Asset Impairment Charges											77,000,000	0	0
Parent Company [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use			$ 23,000,000		$ 49,000,000
Killen [Domain]
Debt Instrument [Line Items]
Assets, fair value		43,000,000		$ 84,000,000		$ 84,000,000					43,000,000
Miami Fort [Domain]
Debt Instrument [Line Items]
Assets, fair value		36,000,000									36,000,000
Zimmer Station [Member]
Debt Instrument [Line Items]
Assets, fair value		24,000,000									24,000,000
DPL Peaking Generation [Domain]
Debt Instrument [Line Items]
Assets, fair value		2,000,000		5,000,000		5,000,000					2,000,000
DPL Subsidiary [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges		624,000,000		$ 235,000,000							859,000,000	0	0
buffalo gap II [Member] [Member]
Debt Instrument [Line Items]
Assets, fair value					92,000,000
Other Asset Impairment Charges											159,000,000	0	0
Stuart Station [Member]
Debt Instrument [Line Items]
Assets, fair value		57,000,000									57,000,000
Kilroot [Member]
Debt Instrument [Line Items]
Assets, fair value									$ 70,000,000
Other Asset Impairment Charges											0	121,000,000	0
Ebute [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges											0	0	67,000,000
Long-Lived Assets													103,000,000
UK Wind (Newfield) [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use													12,000,000
Assets, fair value							$ 0
Other Asset Impairment Charges											0		12,000,000
DP&L (East Bend)
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use													12,000,000
Assets, fair value													2,000,000
Other Asset Impairment Charges											0	0	12,000,000
Conesville DP&L
Debt Instrument [Line Items]
Assets, fair value		$ 1,000,000									1,000,000
buffalo gap III [Member]
Debt Instrument [Line Items]
Assets, fair value										$ 118,000,000
Other Asset Impairment Charges											0	116,000,000	$ 0
UK Wind Development Projects [Domain]
Debt Instrument [Line Items]
Assets, fair value							$ 1,000,000
Other Asset Impairment Charges												$ 37,000,000
number of projects no longer being pursued | project												2
number of impaired projects | project							4
Long-Lived Assets							$ 38,000,000
Long Lived Assets Held And Used [Member] | Fair Value | Ebute [Member]
Debt Instrument [Line Items]
Assets, fair value														$ 36,000,000
Long Lived Assets Held And Used [Member] | Buffalo Gap I
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]							$ 77,000,000
Long Lived Assets Held And Used [Member] | DPL Subsidiary [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]					$ 235,000,000					$ 624,000,000
Long Lived Assets Held And Used [Member] | buffalo gap II [Member] [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]				$ 159,000,000
Long Lived Assets Held And Used [Member] | Kilroot [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]								$ 121,000,000
Long Lived Assets Held And Used [Member] | buffalo gap III [Member]
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]									$ 116,000,000
Long Lived Assets Held And Used [Member] | UK Wind Development Projects [Domain]
Debt Instrument [Line Items]
Other Asset Impairment Charges	[1]						$ 37,000,000

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