Asset Impairment Expense (Impairment of Long-Lived Assets Held and Used by Asset) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Asset impairment expense	$ 537	$ 1,096	$ 285
Impairment of Long-Lived Assets Held-for-use	537	1,096	285
DPL Subsidiary [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	175	859	0
Laurel Mountain [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	121	0	0
Kazakhstan Hydro [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets to be Disposed of	92	0	0
Kazakhstan [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets to be Disposed of	94	0	0
Kilroot [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	37	0	121
buffalo gap III [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	0	116
UK Wind (Newfield) [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	0		37
UK Wind Development Projects [Domain]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use		0	37
buffalo gap II [Member] [Member]
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	159	0
Buffalo Gap I
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	77	0
Other
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 18	$ 1	$ 11